Email alert
RSS2013 Vol. 25, No. 06
Recommend Articles
Display Method:
2013,
25: 1341-1344.
doi: 10.3788/HPLPB20132506.1341
Abstract:
This paper reports a continuous-wave 3.5 m mid-infrared laser based on LD end-pumped Nd:YLF/KTA intra-cavity optical parametric oscillator (OPO). A non-critical phase matching cut KTA crystal with 5 mm5 mm20 mm in size was adopted as the nonlinear optics crystal. A singly resonant oscillator with high reflectivity at signal light was designed to improve the power intensity of the signal light in the OPO cavity and reduce the threshold. The maximum output powers of 335 mW at 3440 nm and 110 mW at 1505 nm were obtained at the pump power of 8.35 W. The total conversion efficiency of 5.6% was achieved with respect to the same incident diode pump power. The results show that continuous-wave KTA-OPO derived by LD pumped solid laser also can produce efficient mid-infrared light.
This paper reports a continuous-wave 3.5 m mid-infrared laser based on LD end-pumped Nd:YLF/KTA intra-cavity optical parametric oscillator (OPO). A non-critical phase matching cut KTA crystal with 5 mm5 mm20 mm in size was adopted as the nonlinear optics crystal. A singly resonant oscillator with high reflectivity at signal light was designed to improve the power intensity of the signal light in the OPO cavity and reduce the threshold. The maximum output powers of 335 mW at 3440 nm and 110 mW at 1505 nm were obtained at the pump power of 8.35 W. The total conversion efficiency of 5.6% was achieved with respect to the same incident diode pump power. The results show that continuous-wave KTA-OPO derived by LD pumped solid laser also can produce efficient mid-infrared light.
2013,
25: 1345-1350.
doi: 10.3788/HPLPB20132506.1345
Abstract:
A method based on superposition of multiple reconstructed images is presented for coherent noise reduction of the phase image in digital holography. The proposed method obtains multiple off-axis holograms upon rotation of the illuminating light in the polar plane under a constant azimuthal angle. Both the tilt factor and lateral shift of the reconstructed phase distribution are compensated by using the phase compensation algorithm and digital image registration method respectively. The coherent noise in the synthesized images is significantly suppressed by averaging reconstructed imaging fields. The experimental results and the related statistical evaluation have demonstrated the effectiveness of this approach.
A method based on superposition of multiple reconstructed images is presented for coherent noise reduction of the phase image in digital holography. The proposed method obtains multiple off-axis holograms upon rotation of the illuminating light in the polar plane under a constant azimuthal angle. Both the tilt factor and lateral shift of the reconstructed phase distribution are compensated by using the phase compensation algorithm and digital image registration method respectively. The coherent noise in the synthesized images is significantly suppressed by averaging reconstructed imaging fields. The experimental results and the related statistical evaluation have demonstrated the effectiveness of this approach.
2013,
25: 1351-1353.
doi: 10.3788/HPLPB20132506.1351
Abstract:
In the video of linear CCD camera being irradiated by 532 nm CW laser, the entirely saturated unilateral smear of laser spot was found. The smear area does not represent the distribution of laser. Since this smear lies merely in one side of laser spot, it can not be induced by light leaking or carriers blooming, and it may be induced by charge transfer loss. However, the feature that the smear area is entirely saturated can not be explained by the current constant model of charge transfer inefficiency. Based on the inner structure and operating principle of buried channel CCD, a new model of charge transfer inefficiency that varies with charge quantity is proposed, which can explain the entirely saturated unilateral smear of laser spot.
In the video of linear CCD camera being irradiated by 532 nm CW laser, the entirely saturated unilateral smear of laser spot was found. The smear area does not represent the distribution of laser. Since this smear lies merely in one side of laser spot, it can not be induced by light leaking or carriers blooming, and it may be induced by charge transfer loss. However, the feature that the smear area is entirely saturated can not be explained by the current constant model of charge transfer inefficiency. Based on the inner structure and operating principle of buried channel CCD, a new model of charge transfer inefficiency that varies with charge quantity is proposed, which can explain the entirely saturated unilateral smear of laser spot.
2013,
25: 1354-1358.
doi: 10.3788/HPLPB20132506.1354
Abstract:
In order to resolve the problem that camouflage target could hardly be detected and identified by the classical means, a spectral polarization detection system was introduced and developed at first. Then the spectral polarization experiment about the bottle green and khaki camouflage coatings in grassplot and soil were conducted by the system at the wavelengths of 442.0, 545.5, 670.5, 850.5 nm. The polarization images were deduced by the polarization information process software through processing the experiment data captured by the system. The change rule about the degree of the polarization and the polarization contrast of the target and background was discovered. The calculated result shows that by choosing proper detection condition the polarization contrast between camouflage coating and background could be enhanced. Consequently, the classical camouflage target can be detected and identified effectively by the spectral polarization system.
In order to resolve the problem that camouflage target could hardly be detected and identified by the classical means, a spectral polarization detection system was introduced and developed at first. Then the spectral polarization experiment about the bottle green and khaki camouflage coatings in grassplot and soil were conducted by the system at the wavelengths of 442.0, 545.5, 670.5, 850.5 nm. The polarization images were deduced by the polarization information process software through processing the experiment data captured by the system. The change rule about the degree of the polarization and the polarization contrast of the target and background was discovered. The calculated result shows that by choosing proper detection condition the polarization contrast between camouflage coating and background could be enhanced. Consequently, the classical camouflage target can be detected and identified effectively by the spectral polarization system.
2013,
25: 1359-1364.
doi: 10.3788/HPLPB20132506.1359
Abstract:
According to the reaction mechanism of laser beam, powder particles and melting pool during the laser cladding process, a mathematical model of powder utilization efficiency was formulated. A quantitive expression describing the relation between the powder injection angle and the contour parameters of laser cladding coating was obtained. Based on thermo-physical properties of Fe55 alloy powder and laser cladding process parameters, the powder utilization efficiency, cladding coating height and cross-section area were calculated by means of AutoCAD software. The results show that the powder utilization efficiency, and cladding coating height and cross-section area increase with the powder injection angle increasing, and theoretically calculated values are larger than the experimental values. Owing to powder burning and mechanical losing in the process of laser cladding, the powder utilization efficiency, and cladding coating height and cross-section area reach their maxima simultaneously with the variation of powder injection angle. The ideal powder injection angle is 60.
According to the reaction mechanism of laser beam, powder particles and melting pool during the laser cladding process, a mathematical model of powder utilization efficiency was formulated. A quantitive expression describing the relation between the powder injection angle and the contour parameters of laser cladding coating was obtained. Based on thermo-physical properties of Fe55 alloy powder and laser cladding process parameters, the powder utilization efficiency, cladding coating height and cross-section area were calculated by means of AutoCAD software. The results show that the powder utilization efficiency, and cladding coating height and cross-section area increase with the powder injection angle increasing, and theoretically calculated values are larger than the experimental values. Owing to powder burning and mechanical losing in the process of laser cladding, the powder utilization efficiency, and cladding coating height and cross-section area reach their maxima simultaneously with the variation of powder injection angle. The ideal powder injection angle is 60.
2013,
25: 1365-1369.
doi: 10.3788/HPLPB20132506.1365
Abstract:
In order to improve the imaging quality of pre-magnification digital holography, the imaging systems of pre-magnification digital holography with the plane wave and spherical wave respectively as the reference light are studied and compared theoretically and experimentally. The results show that, the lateral resolution of the two systems mainly depends on the resolution of microscopic lens in general experimental conditions. When the recording distance is short, the lateral resolution of both systems will be slightly lower with the recording distance increasing; and when the recording distance is comparatively large, the resolution of the system with spherical wave as the reference light is worse, scilicet, the system of plane wave is relatively superior. As the recording distance of the hologram is zero, which is named as digital image-plane holography, the resolution of reconstructed image is best. When an ordinary industrial sensor is adopted, the lateral resolution far exceeds 2.19 m, and the image quality is fairly good. Reducing the recording distance of digital hologram as much as possible, or employing the digital image-plane holography, can improve the imaging resolution of digital holography.
In order to improve the imaging quality of pre-magnification digital holography, the imaging systems of pre-magnification digital holography with the plane wave and spherical wave respectively as the reference light are studied and compared theoretically and experimentally. The results show that, the lateral resolution of the two systems mainly depends on the resolution of microscopic lens in general experimental conditions. When the recording distance is short, the lateral resolution of both systems will be slightly lower with the recording distance increasing; and when the recording distance is comparatively large, the resolution of the system with spherical wave as the reference light is worse, scilicet, the system of plane wave is relatively superior. As the recording distance of the hologram is zero, which is named as digital image-plane holography, the resolution of reconstructed image is best. When an ordinary industrial sensor is adopted, the lateral resolution far exceeds 2.19 m, and the image quality is fairly good. Reducing the recording distance of digital hologram as much as possible, or employing the digital image-plane holography, can improve the imaging resolution of digital holography.
2013,
25: 1370-1374.
doi: 10.3788/HPLPB20132506.1370
Abstract:
To study the effect of oil phase and water phase on the wall thickness in the emulsion encapsulation method, an expression of the wall thickness varying with the polymer mass fraction in oil phase and the volume ratio of polymer solution and inner water has been deduced in the ideal state. It is shown that the wall thickness increases with increasing the polymer mass fraction or the volume ratio of polymer solution and inner water. Therefore, the wall thickness can be controlled by adjusting either the polymer mass fraction or the volume ratio of polymer solution and inner water. According to the rule, the optimal parameter values are obtained by varying the parameters of oil phase and water phase in the agitation method for preparing hollow polystyrene (PS) microspheres. The experimental results show that, in order to prepare PS microspheres with 10 m to 25 m wall thickness, the PS mass fraction should be controlled in the range of 5.3% to 7.0% while the volume ratio of PS solution and inner water should be within the range of 1.6 to 2.2. Moreover, the optimal range of PVA mass fraction in outer water is between 1% and 3%.
To study the effect of oil phase and water phase on the wall thickness in the emulsion encapsulation method, an expression of the wall thickness varying with the polymer mass fraction in oil phase and the volume ratio of polymer solution and inner water has been deduced in the ideal state. It is shown that the wall thickness increases with increasing the polymer mass fraction or the volume ratio of polymer solution and inner water. Therefore, the wall thickness can be controlled by adjusting either the polymer mass fraction or the volume ratio of polymer solution and inner water. According to the rule, the optimal parameter values are obtained by varying the parameters of oil phase and water phase in the agitation method for preparing hollow polystyrene (PS) microspheres. The experimental results show that, in order to prepare PS microspheres with 10 m to 25 m wall thickness, the PS mass fraction should be controlled in the range of 5.3% to 7.0% while the volume ratio of PS solution and inner water should be within the range of 1.6 to 2.2. Moreover, the optimal range of PVA mass fraction in outer water is between 1% and 3%.
2013,
25: 1375-1378.
doi: 10.3788/HPLPB20132506.1375
Abstract:
The diamond phase fraction, optical constant and hardness of diamond-like carbon thin films deposited at different radio frequency powers by radio frequency plasma chemical vapor deposition have been investigated. The diamond phase fraction, optical constant and hardness of single-layered thin films at different radio frequency powers have been measured by using Raman spectroscopy, spectroscopic ellipsometer and micro-sclerometer, respectively. With the increase of radio frequency power, the fraction of diamond phase decreases and the growth rate of films increases, especially when the power is above 910 W. The refractive index of films decreases in the range of 660-860 W and 910-960 W and increases between 860 W and 910 W. The hardness increases and then decreases between 660 W and 960 W with its maximum at 860 W.
The diamond phase fraction, optical constant and hardness of diamond-like carbon thin films deposited at different radio frequency powers by radio frequency plasma chemical vapor deposition have been investigated. The diamond phase fraction, optical constant and hardness of single-layered thin films at different radio frequency powers have been measured by using Raman spectroscopy, spectroscopic ellipsometer and micro-sclerometer, respectively. With the increase of radio frequency power, the fraction of diamond phase decreases and the growth rate of films increases, especially when the power is above 910 W. The refractive index of films decreases in the range of 660-860 W and 910-960 W and increases between 860 W and 910 W. The hardness increases and then decreases between 660 W and 960 W with its maximum at 860 W.
2013,
25: 1379-1382.
doi: 10.3788/HPLPB20132506.1379
Abstract:
Using the reference frame transformation, radiation damping effects in ultra-intense laser-plasma interaction are analyzed based on the motion equation of a radiation electron. The results show that, in both cases of the circularly and the linearly polarized lasers, the radiation damping effects are enhanced with the plasma density increasing. In the circularly polarization case, if the laser intensity is at the order of 1023-1026 W/cm2, corresponding to different plasma densities, the radiation damping effects may influence the motion of electron significantly, while in the linearly polarization case, only when the laser intensity is much higher than the critical intensity, the radiation damping effects can obviously affect the motion of electron.
Using the reference frame transformation, radiation damping effects in ultra-intense laser-plasma interaction are analyzed based on the motion equation of a radiation electron. The results show that, in both cases of the circularly and the linearly polarized lasers, the radiation damping effects are enhanced with the plasma density increasing. In the circularly polarization case, if the laser intensity is at the order of 1023-1026 W/cm2, corresponding to different plasma densities, the radiation damping effects may influence the motion of electron significantly, while in the linearly polarization case, only when the laser intensity is much higher than the critical intensity, the radiation damping effects can obviously affect the motion of electron.
2013,
25: 1383-1386.
Abstract:
Based on electro-optical theory and adiabatic compression theory, a double-anode magnetic injection gun for TE34,19，170 GHz gyrotron was analyzed and designed with EGUN software. Concerning with the factors such as positions of anode and magnetic field distance between anodes, we obtained the result that the velocity ratio of electron beam approximated 1.3, and the velocity spread was under 3%. Furthermore, we found that electron beam was sensitive with these factors, such as that the velocity ratio decreased when the distance between anodes increased, while the velocity spread decreased first and then increased. The double-anode magnetic injection gun is employed in the experiments of gyrotron.
Based on electro-optical theory and adiabatic compression theory, a double-anode magnetic injection gun for TE34,19，170 GHz gyrotron was analyzed and designed with EGUN software. Concerning with the factors such as positions of anode and magnetic field distance between anodes, we obtained the result that the velocity ratio of electron beam approximated 1.3, and the velocity spread was under 3%. Furthermore, we found that electron beam was sensitive with these factors, such as that the velocity ratio decreased when the distance between anodes increased, while the velocity spread decreased first and then increased. The double-anode magnetic injection gun is employed in the experiments of gyrotron.
2013,
25: 1387-1390.
Abstract:
To improve the performance of high power microwave (HPM) antennas, a novel X-band left-handed material planar radome is developed. The measurement results of this radome show that the beam of a antenna can be focused by using the left-handed material radome with 1-4 layers in the frequency range of 9.0-9.4 GHz, and the gain of the antenna can be raised by about 9.64 dB at 9.32 GHz for the radome with one layer. But the experimental data do not agree well with the theoretical simulation. The analysis of the power capacity of the radome indicates that the radome could be applied to HPM field.
To improve the performance of high power microwave (HPM) antennas, a novel X-band left-handed material planar radome is developed. The measurement results of this radome show that the beam of a antenna can be focused by using the left-handed material radome with 1-4 layers in the frequency range of 9.0-9.4 GHz, and the gain of the antenna can be raised by about 9.64 dB at 9.32 GHz for the radome with one layer. But the experimental data do not agree well with the theoretical simulation. The analysis of the power capacity of the radome indicates that the radome could be applied to HPM field.
2013,
25: 1391-1395.
doi: 10.3788/HPLPB20132506.1391
Abstract:
The power series method is used to analyze the nonlinear distortion characteristics of the predistortion linearizer which are contrary to the distortion characteristics of the travelling wave tube amplifier(TWTA), and also the model of the predistortion linearizer is proposed. As anti-parallel Schottky diodes can produce odd-order harmonics, a reflective predistortion linearizer for Ka-band TWTA is designed using the structures of anti-parallel schottky diodes, quadrature hybrid bridges and matching networks. The result of experiment shows that 19 dB improvement is introduced to the carrier-to-intermodulation ratio of the TWTA which reaches and even exceeds the demand.
The power series method is used to analyze the nonlinear distortion characteristics of the predistortion linearizer which are contrary to the distortion characteristics of the travelling wave tube amplifier(TWTA), and also the model of the predistortion linearizer is proposed. As anti-parallel Schottky diodes can produce odd-order harmonics, a reflective predistortion linearizer for Ka-band TWTA is designed using the structures of anti-parallel schottky diodes, quadrature hybrid bridges and matching networks. The result of experiment shows that 19 dB improvement is introduced to the carrier-to-intermodulation ratio of the TWTA which reaches and even exceeds the demand.
2013,
25: 1396-1400.
doi: 10.3788/HPLPB20132506.1396
Abstract:
Bremsstrahlung source with high energy electrons will produce a substantial excess of high energy photons, and these photons and electrons severely degrade the fidelity of system generated electromagnetic pulse(SGEMP) simulations. Thus, the development of composite thin converter were undertaken to achieve a high fidelity of X-ray source, using high Z material with small thickness to lower photon energy and low Z material to filter the transmission electrons. The influence of converter thickness on X-ray parameters was analyzed by using MCNP code. And a composite converter was designed for flash-Ⅱ accelerator based on the simulation result. Experimental result shows that the average energy of photons is 121 keV, the dose on 700 cm2 area is more than 40 rad(Si) and it is 170 rad(Si) on 500 cm2 area. The uniformity is less than 2∶1, and the ratio of photons to electrons is more than 103. The proportion of the number of photons whose energy is less than 120 keV in total photons is 69 percent, and the proportion of energy is 58 percent in the same case. The proportions of simulation result are respectively 70 percent and 65 percent, which are close to the experimental result. The X-ray source can be used for SGEMP simulations and the design method of converter can be used to lower photon energy for other X-ray sources.
Bremsstrahlung source with high energy electrons will produce a substantial excess of high energy photons, and these photons and electrons severely degrade the fidelity of system generated electromagnetic pulse(SGEMP) simulations. Thus, the development of composite thin converter were undertaken to achieve a high fidelity of X-ray source, using high Z material with small thickness to lower photon energy and low Z material to filter the transmission electrons. The influence of converter thickness on X-ray parameters was analyzed by using MCNP code. And a composite converter was designed for flash-Ⅱ accelerator based on the simulation result. Experimental result shows that the average energy of photons is 121 keV, the dose on 700 cm2 area is more than 40 rad(Si) and it is 170 rad(Si) on 500 cm2 area. The uniformity is less than 2∶1, and the ratio of photons to electrons is more than 103. The proportion of the number of photons whose energy is less than 120 keV in total photons is 69 percent, and the proportion of energy is 58 percent in the same case. The proportions of simulation result are respectively 70 percent and 65 percent, which are close to the experimental result. The X-ray source can be used for SGEMP simulations and the design method of converter can be used to lower photon energy for other X-ray sources.
2013,
25: 1401-1404.
doi: 10.3788/HPLPB20132506.1401
Abstract:
A 200-kV flash X-ray radiographic test system based on the principle of Marx generator is introduced. The system has a delay function that it can produce X rays at predetermined time in accordance with the experimental requirement. A 10-stage 200-kV Marx generator has been designed in coaxial structure, and low-jitter field-distortion switches, low-inductance solid-state resistors and ceramic capacitors are used in the pulse generator to shorten the risetime and pulse width of output pulses. The generator was demonstrated to deliver pulses of more than 200 kV onto a 75- load with 100-ns pulse width. Being connected with an X-ray tube through a high-voltage cable, the pulse generator drove the X-ray tube to produce flash X-rays with a pulse width of 70 ns and a dose of 910-6 C/kg at the distance of 0.25 m from the laser source.
A 200-kV flash X-ray radiographic test system based on the principle of Marx generator is introduced. The system has a delay function that it can produce X rays at predetermined time in accordance with the experimental requirement. A 10-stage 200-kV Marx generator has been designed in coaxial structure, and low-jitter field-distortion switches, low-inductance solid-state resistors and ceramic capacitors are used in the pulse generator to shorten the risetime and pulse width of output pulses. The generator was demonstrated to deliver pulses of more than 200 kV onto a 75- load with 100-ns pulse width. Being connected with an X-ray tube through a high-voltage cable, the pulse generator drove the X-ray tube to produce flash X-rays with a pulse width of 70 ns and a dose of 910-6 C/kg at the distance of 0.25 m from the laser source.
2013,
25: 1405-1408.
doi: 10.3788/HPLPB20132506.1405
Abstract:
Two GaAs/AlxGa1-xAs infrared quantum well materials with different structure parameters have been made by using metal organic chemical vapor deposition. The photoresponse spectra are obtained at 77 K by use of Fourier transform spectrometer for two sample-devices of GaAs/AlxGa1-xAs quantum well infrared photodetectors with an Al content of 0.20 and 0.30 respectively. The results show the peak wavelengths of 1# and 2# are 8.38 m and 7.59 m, while they are 9.694 m and 8.134 m according to the Schrdinger equation, and the errors between them are 13.6%, 6.68%, respectively. The crystal structure is investigated by using high-resolution scanning transmission electron microscope to analyse the main reason of the large errors and peak wavelength redshift, which shows that there is thread dislocation and nonuniformity in different degrees. The main reason causing 1# error much larger is the crystal lattice mismatch between AlGaAs and GaAs. The fact that the peak wavelength increases with Al content reducing shows reducing Al content will lead to narrowing of the spacing between subbands and peak wavelength redshift.
Two GaAs/AlxGa1-xAs infrared quantum well materials with different structure parameters have been made by using metal organic chemical vapor deposition. The photoresponse spectra are obtained at 77 K by use of Fourier transform spectrometer for two sample-devices of GaAs/AlxGa1-xAs quantum well infrared photodetectors with an Al content of 0.20 and 0.30 respectively. The results show the peak wavelengths of 1# and 2# are 8.38 m and 7.59 m, while they are 9.694 m and 8.134 m according to the Schrdinger equation, and the errors between them are 13.6%, 6.68%, respectively. The crystal structure is investigated by using high-resolution scanning transmission electron microscope to analyse the main reason of the large errors and peak wavelength redshift, which shows that there is thread dislocation and nonuniformity in different degrees. The main reason causing 1# error much larger is the crystal lattice mismatch between AlGaAs and GaAs. The fact that the peak wavelength increases with Al content reducing shows reducing Al content will lead to narrowing of the spacing between subbands and peak wavelength redshift.
2013,
25: 1409-1413.
doi: 10.3788/HPLPB20132506.1409
Abstract:
The stacked Blumlein line has significant potential to be applied in the high-power compact pulsed generator. The analytical expression of the output pulse for a lossless stacked Blumlein line is obtained by using Laplace transform in this paper. A two-port network model of transmission line is applied to deriving the expressions of transmission line characteristic impedance in frequency domain for shorted and open load terminals. Based on the previous results, a circuit schematic of a single Blumlein line is simplified, and the expression of the output voltage pulse is also obtained. Then the analytical expression of the output voltage pulse of a 2-stage stacked Blumlein line in time domain is determined through adopting the superposition principle of circuit. Finally, the analytical expression in the case of arbitrary stage-number is given by using a recurrence method.
The stacked Blumlein line has significant potential to be applied in the high-power compact pulsed generator. The analytical expression of the output pulse for a lossless stacked Blumlein line is obtained by using Laplace transform in this paper. A two-port network model of transmission line is applied to deriving the expressions of transmission line characteristic impedance in frequency domain for shorted and open load terminals. Based on the previous results, a circuit schematic of a single Blumlein line is simplified, and the expression of the output voltage pulse is also obtained. Then the analytical expression of the output voltage pulse of a 2-stage stacked Blumlein line in time domain is determined through adopting the superposition principle of circuit. Finally, the analytical expression in the case of arbitrary stage-number is given by using a recurrence method.
2013,
25: 1414-1418.
doi: 10.3788/HPLPB20132506.1414
Abstract:
This paper presents a pulse forming network(PFN) stacked Blumlein pulse generator commutated by a single switch, in which the PFN is composed of ceramic capacitors and plate conductors. The shorted discharging characteristic of the shorted parasitic transmission line was analyzed in theory. Results show that the shorted parasitic transmission line could be replaced by a shorted inductor. Equivalent circuit models were simulated using Pspice code to compare the effect of the shorted parasitic transmission line with that of the shorted inductor. Simulation results show that the increase in the inductance of the shorted parasitic transmission line could improve the voltage efficiency. A four-stage stacked Blumlein pulse generator with magnetic cores was designed to increase the shorted inductance. Its voltage gain reaches 3.1 on the matched load.
This paper presents a pulse forming network(PFN) stacked Blumlein pulse generator commutated by a single switch, in which the PFN is composed of ceramic capacitors and plate conductors. The shorted discharging characteristic of the shorted parasitic transmission line was analyzed in theory. Results show that the shorted parasitic transmission line could be replaced by a shorted inductor. Equivalent circuit models were simulated using Pspice code to compare the effect of the shorted parasitic transmission line with that of the shorted inductor. Simulation results show that the increase in the inductance of the shorted parasitic transmission line could improve the voltage efficiency. A four-stage stacked Blumlein pulse generator with magnetic cores was designed to increase the shorted inductance. Its voltage gain reaches 3.1 on the matched load.
2013,
25: 1419-1426.
doi: 10.3788/HPLPB20132506.1419
Abstract:
Based on a large-scale parallel code named NEPTUNE3D for 3D fully electromagnetic and PIC simulations programmed by our group, we design and develop a Finite Conductivity Wall (FCW) module in order to simulate the gain loss phenomenon in THz traveling-wave tube caused by metal conductivity and roughness. First, the advantage and disadvantage of FDTD scheme in metal material and harmonious conditions are introduced. Then, we put forward an implicit scheme of FCW and discuss its numerical flow. This method is of unconditional stability and good expansibility. Moreover, we test the FCW module with an example of electromagnetic wave mode transmission in a rectangular wave guide. Compared with theoretical results and commercial electromagnetic software simulation results, the FCW module is validated. By using the improved NEPTUNE3D code after adding FCW module, we simulate an 0.22 THz folded-waveguide traveling-wave tube (FWTWT) gain loss course caused by copper surface roughness. The simulation results indicate that metal surface roughness causes a serious gain loss effect on FWTWT device. Finally, the dispersion relation, interaction impedance and attenuation of device are analyzed, some structure design advices are presented. For increasing the output power, increasing signal power, beam current and structure period number is feasible in some ways.
Based on a large-scale parallel code named NEPTUNE3D for 3D fully electromagnetic and PIC simulations programmed by our group, we design and develop a Finite Conductivity Wall (FCW) module in order to simulate the gain loss phenomenon in THz traveling-wave tube caused by metal conductivity and roughness. First, the advantage and disadvantage of FDTD scheme in metal material and harmonious conditions are introduced. Then, we put forward an implicit scheme of FCW and discuss its numerical flow. This method is of unconditional stability and good expansibility. Moreover, we test the FCW module with an example of electromagnetic wave mode transmission in a rectangular wave guide. Compared with theoretical results and commercial electromagnetic software simulation results, the FCW module is validated. By using the improved NEPTUNE3D code after adding FCW module, we simulate an 0.22 THz folded-waveguide traveling-wave tube (FWTWT) gain loss course caused by copper surface roughness. The simulation results indicate that metal surface roughness causes a serious gain loss effect on FWTWT device. Finally, the dispersion relation, interaction impedance and attenuation of device are analyzed, some structure design advices are presented. For increasing the output power, increasing signal power, beam current and structure period number is feasible in some ways.
2013,
25: 1427-1430.
doi: 10.3788/HPLPB20132506.1427
Abstract:
The carrier absorption of the doped semiconductor materials is evident in terahertz (THz). The reciprocity study is the basis for preparing the key apparatus in the THz communications. Using a pulsed KrF excimer laser ablation (PLD) technique, the Ni-doped BaTiO3/SrTiO3 multilayer film has been prepared. Based on 3.09 THz quantum cascade laser (QCL) with the peak optical power about 10 mW, the transition of THz waves in the Ni-doped BaTiO3/SrTiO3 multilayer films is studied. It is found that the main loss may be due to the nonresonant absorption of Ni particles.
The carrier absorption of the doped semiconductor materials is evident in terahertz (THz). The reciprocity study is the basis for preparing the key apparatus in the THz communications. Using a pulsed KrF excimer laser ablation (PLD) technique, the Ni-doped BaTiO3/SrTiO3 multilayer film has been prepared. Based on 3.09 THz quantum cascade laser (QCL) with the peak optical power about 10 mW, the transition of THz waves in the Ni-doped BaTiO3/SrTiO3 multilayer films is studied. It is found that the main loss may be due to the nonresonant absorption of Ni particles.
2013,
25: 1431-1434.
doi: 10.3788/HPLPB20132506.1431
Abstract:
CO2 laser pump source is one of the most important core components of optically pumped THz gas laser, and its performance will directly affect the stability of the THz laser. A blazed grating is generally employed as a total reflecting tail mirror to constitute a grating resonator. The intra-cavity beam modes in the grating resonator are numerically studied with the transit matrix eigenvector method in this paper. A series of eigenmodes and the corresponding diffraction losses are calculated. It is shown that the characteristics of the intra-cavity eigenmode in a grating resonator are equivalent to those of a plane-concave resonator. For the grating resonator with a large Fresnel number, the diffraction loss of the lowest order mode in the vicinity of the Littrow wavelength may be lower than that of the higher order modes at the Littrow wavelength. In that case, the discrimination of the output longitudinal mode becomes weak.
CO2 laser pump source is one of the most important core components of optically pumped THz gas laser, and its performance will directly affect the stability of the THz laser. A blazed grating is generally employed as a total reflecting tail mirror to constitute a grating resonator. The intra-cavity beam modes in the grating resonator are numerically studied with the transit matrix eigenvector method in this paper. A series of eigenmodes and the corresponding diffraction losses are calculated. It is shown that the characteristics of the intra-cavity eigenmode in a grating resonator are equivalent to those of a plane-concave resonator. For the grating resonator with a large Fresnel number, the diffraction loss of the lowest order mode in the vicinity of the Littrow wavelength may be lower than that of the higher order modes at the Littrow wavelength. In that case, the discrimination of the output longitudinal mode becomes weak.
2013,
25: 1435-1439.
doi: 10.3788/HPLPB20132506.1435
Abstract:
With the development of the power capacity of 110 GHz high-power terahertz waves, the air breakdown by 110 GHz high-power terahertz waves has drawn more and more attention. Several approximations of effective ionization parameters are introduced into the equation of the electron avalanche density, and the breakdown thresholds are calculated at different pressures. The results show that the breakdown thresholds from Ali effective ionization parameters agree very well with the experimental result. The dependence of transmitted energy density on the electric amplitude is also investigated using Ali effective ionization parameters. The results show that, the transmitted energy density increases with the power density linearly when the amplitude is lower than the breakdown threshold; but the transmitted energy density first increases with the amplitude and then decreases when the amplitude is larger than the breakdown threshold.
With the development of the power capacity of 110 GHz high-power terahertz waves, the air breakdown by 110 GHz high-power terahertz waves has drawn more and more attention. Several approximations of effective ionization parameters are introduced into the equation of the electron avalanche density, and the breakdown thresholds are calculated at different pressures. The results show that the breakdown thresholds from Ali effective ionization parameters agree very well with the experimental result. The dependence of transmitted energy density on the electric amplitude is also investigated using Ali effective ionization parameters. The results show that, the transmitted energy density increases with the power density linearly when the amplitude is lower than the breakdown threshold; but the transmitted energy density first increases with the amplitude and then decreases when the amplitude is larger than the breakdown threshold.
2013,
25: 1440-1444.
doi: 10.3788/HPLPB20132506.1440
Abstract:
The subwavelength semiconductor sphere arrays in THz range are simulated with T-matrix method. Based on the numerical results, their optical properties are also discussed. The properties of semiconductor surface plasmon can be tailored within the terahertz frequency range through doping. We take the semiconductor InSb as an example and adopt Drude model for simulating single subwavelength sphere and arrays with two or more subwavelength spheres. In addition, we discuss the effects of some parameters on the properties of sphere arrays, such as the sphere radius, periodicity of the array, the number of spheres in the array and the polarization direction of the incident wave. The result gives a preliminary comprehension on the optical properties of subwavelength semiconductor sphere arrays and provides some theoretical help for their potential applications.
The subwavelength semiconductor sphere arrays in THz range are simulated with T-matrix method. Based on the numerical results, their optical properties are also discussed. The properties of semiconductor surface plasmon can be tailored within the terahertz frequency range through doping. We take the semiconductor InSb as an example and adopt Drude model for simulating single subwavelength sphere and arrays with two or more subwavelength spheres. In addition, we discuss the effects of some parameters on the properties of sphere arrays, such as the sphere radius, periodicity of the array, the number of spheres in the array and the polarization direction of the incident wave. The result gives a preliminary comprehension on the optical properties of subwavelength semiconductor sphere arrays and provides some theoretical help for their potential applications.
2013,
25: 1445-1449.
doi: 10.3788/HPLPB20132506.1445
Abstract:
The atmosphere is opaque to terahertz wave, hence knowing accurately the location and width of atmospheric transmission windows is crucial to facilitating any type of applications utilizing THz technology. In this paper, the line-by-line integral method is used to calculate the THz atmospheric transmittance attenuation. Based on the molecular line data provided by HITRAN 2008 database, the calculation results of the attenuation characteristics of H2O, O2, O3, CO2 and N2 gas with certain density, temperature and pressure are presented and discussed. The results indicate that vapor and oxygen contribute the most to THz transmittance attenuation under the natural conditions in the 0-3 THz range.
The atmosphere is opaque to terahertz wave, hence knowing accurately the location and width of atmospheric transmission windows is crucial to facilitating any type of applications utilizing THz technology. In this paper, the line-by-line integral method is used to calculate the THz atmospheric transmittance attenuation. Based on the molecular line data provided by HITRAN 2008 database, the calculation results of the attenuation characteristics of H2O, O2, O3, CO2 and N2 gas with certain density, temperature and pressure are presented and discussed. The results indicate that vapor and oxygen contribute the most to THz transmittance attenuation under the natural conditions in the 0-3 THz range.
2013,
25: 1450-1454.
doi: 10.3788/HPLPB20132506.1450
Abstract:
Through theoretical analysis and PIC simulation, beam emittances of 140, 220 and 345 GHz FWG-TWTs are studied. The relationships of beam emittance with frequency, structure size and even the related parameters of electron beam are summarized. It is shown that beam emittance is an important parameter determining the design of focusing magnetic field in the terahertz band.
Through theoretical analysis and PIC simulation, beam emittances of 140, 220 and 345 GHz FWG-TWTs are studied. The relationships of beam emittance with frequency, structure size and even the related parameters of electron beam are summarized. It is shown that beam emittance is an important parameter determining the design of focusing magnetic field in the terahertz band.
2013,
25: 1455-1459.
doi: 10.3788/HPLPB20132506.1455
Abstract:
The scheme of elliptical hole-coupling optical resonator is proposed instead of circular hole-coupling resonator which is used in THz FEL in order to increase the output power and resonator quality. Three-dimensional simulations and design on elliptical hole-coupling optical resonator are carried out using our 3D OSIFEL code. It is proved that the elliptical hole-coupling optical resonator is effective and applicable for the THz FEL. Using elliptical hole-coupling optical resonator, the output power can be increased by more than 33%, and the coupling efficiency of resonator can be increased almost by 30%-70%. The superiority of elliptical hole-coupling optical resonator will be more prominent with radiation frequency increasing.
The scheme of elliptical hole-coupling optical resonator is proposed instead of circular hole-coupling resonator which is used in THz FEL in order to increase the output power and resonator quality. Three-dimensional simulations and design on elliptical hole-coupling optical resonator are carried out using our 3D OSIFEL code. It is proved that the elliptical hole-coupling optical resonator is effective and applicable for the THz FEL. Using elliptical hole-coupling optical resonator, the output power can be increased by more than 33%, and the coupling efficiency of resonator can be increased almost by 30%-70%. The superiority of elliptical hole-coupling optical resonator will be more prominent with radiation frequency increasing.
2013,
25: 1460-1464.
doi: 10.3788/HPLPB20132506.1460
Abstract:
The intersubband optical absorption of a semiconductor quantum well driven by an in-plane terahertz electric field is investigated theoretically by employing the extended semiconductor Bloch equations. Our results show that in-plane polarized terahertz fields induce a variety of behavior in the absorption spectra, including terahertz replicas of the main absorption peak and the dynamical Franz-Keldysh effect. The dependence of the absorption of the probe field on frequency and phase of the terahertz field is also very remarkable.
The intersubband optical absorption of a semiconductor quantum well driven by an in-plane terahertz electric field is investigated theoretically by employing the extended semiconductor Bloch equations. Our results show that in-plane polarized terahertz fields induce a variety of behavior in the absorption spectra, including terahertz replicas of the main absorption peak and the dynamical Franz-Keldysh effect. The dependence of the absorption of the probe field on frequency and phase of the terahertz field is also very remarkable.
2013,
25: 1465-1468.
doi: 10.3788/HPLPB20132506.1465
Abstract:
A miniature extracavity terahertz(THz) parametric oscillator is proposed based on surface-emitted technology. Using a small sized pulsed laser to pump MgO:LiNbO3 crystal, the THz-wave is emitted perpendicularly to the crystal surface by optimization design of three-wave non-collinear phase-matching optical parametric oscillation structure. This configuration can reduce the absorption of the THz-wave and improve the beam quality. The THz-wave can be tuned from 0.69 THz to 3.01 THz. When the pump energy is 128 mJ, the maximum average power of the THz-wave is 10.8 W at 1.6 THz , corresponding to an energy conversion efficiency of 8.4310-6. This room-temperature-operated, miniature system is suited to a variety of applications such as spectral analysis and THz communications.
A miniature extracavity terahertz(THz) parametric oscillator is proposed based on surface-emitted technology. Using a small sized pulsed laser to pump MgO:LiNbO3 crystal, the THz-wave is emitted perpendicularly to the crystal surface by optimization design of three-wave non-collinear phase-matching optical parametric oscillation structure. This configuration can reduce the absorption of the THz-wave and improve the beam quality. The THz-wave can be tuned from 0.69 THz to 3.01 THz. When the pump energy is 128 mJ, the maximum average power of the THz-wave is 10.8 W at 1.6 THz , corresponding to an energy conversion efficiency of 8.4310-6. This room-temperature-operated, miniature system is suited to a variety of applications such as spectral analysis and THz communications.
2013,
25: 1469-1474.
doi: 10.3788/HPLPB20132506.1469
Abstract:
Terahertz inverse synthetic aperture radar (THz-ISAR) works at high frequency band with short wavelength and large bandwidth. Compared to ISAR operated in microwave band, THz-ISAR is more susceptible to the phase error which will cause the spread and shift of range profiles, thus affect the quality of the two-dimensional (2-D) high resolution image. Based on detailed analysis of the echo model, a method of second order phase error compensation was proposed based on minimizing the entropy of range profiles through enlightened search. In the meantime, another method based on range autofocusing was utilized to compensate the third or higher order phase error. After compensating the phase error through the above methods, well focused high resolution range profiles (HRRPs) and high resolution images were obtained using range-Doppler (RD) algorithm. Theoretical analysis and simulated results verified the effectiveness of this method.
Terahertz inverse synthetic aperture radar (THz-ISAR) works at high frequency band with short wavelength and large bandwidth. Compared to ISAR operated in microwave band, THz-ISAR is more susceptible to the phase error which will cause the spread and shift of range profiles, thus affect the quality of the two-dimensional (2-D) high resolution image. Based on detailed analysis of the echo model, a method of second order phase error compensation was proposed based on minimizing the entropy of range profiles through enlightened search. In the meantime, another method based on range autofocusing was utilized to compensate the third or higher order phase error. After compensating the phase error through the above methods, well focused high resolution range profiles (HRRPs) and high resolution images were obtained using range-Doppler (RD) algorithm. Theoretical analysis and simulated results verified the effectiveness of this method.
2013,
25: 1475-1478.
doi: 10.3788/HPLPB20132506.1475
Abstract:
A novel fabrication technique for high density gate hole arrays used in field emission cold cathodes is present here. This technique has been implemented by combining the micro electromechanical system (MEMS) processes with the microsphere lithography. Microsphere photolithography (MSP) generates a large area of highly uniform periodic sub-micrometer spot arrays by utilizing the monolayer of polystyrene (PS) latex microspheres as mask on top of silicon or silica. A large area of highly uniform sub-micrometer grid hole arrays (300-600 nm) with the array period of 0.75 m can be fabricated by the combination of lift-off and MSP. Microhole array density reaches to 108 holes/cm2. This is a promising method to fabricate a large area of highly uniform periodic and high-density gate hole arrays for field emission cold cathodes. The period is restricted by the microsphere diameter. The gate aperture can be tuned by shrinking the PS sphere using O2 reaction ion etching (RIE).
A novel fabrication technique for high density gate hole arrays used in field emission cold cathodes is present here. This technique has been implemented by combining the micro electromechanical system (MEMS) processes with the microsphere lithography. Microsphere photolithography (MSP) generates a large area of highly uniform periodic sub-micrometer spot arrays by utilizing the monolayer of polystyrene (PS) latex microspheres as mask on top of silicon or silica. A large area of highly uniform sub-micrometer grid hole arrays (300-600 nm) with the array period of 0.75 m can be fabricated by the combination of lift-off and MSP. Microhole array density reaches to 108 holes/cm2. This is a promising method to fabricate a large area of highly uniform periodic and high-density gate hole arrays for field emission cold cathodes. The period is restricted by the microsphere diameter. The gate aperture can be tuned by shrinking the PS sphere using O2 reaction ion etching (RIE).
2013,
25: 1479-1482.
doi: 10.3788/HPLPB20132506.1479
Abstract:
Several metal hole array(MHA) structures of different sizes and shapes in THz were designed. The detection sensitivity of the structures with ultra-thin and low refractive index polyimide films, was explored on a THz time-domain system. MHAs with different structures were fabricated with femtosecond micromachining technology, and the THz reflection spectra were measured by the THz time-domain system. By attaching an ultra-thin polyimide (10 m) film to the MHA, an obvious blue-shift of reflective resonance peak was observed, which indicated a high sensitivity of MHA to low refractive index materials. This characteristic allows us to achieve MHA-based high-sensitive sensor at THz band.
Several metal hole array(MHA) structures of different sizes and shapes in THz were designed. The detection sensitivity of the structures with ultra-thin and low refractive index polyimide films, was explored on a THz time-domain system. MHAs with different structures were fabricated with femtosecond micromachining technology, and the THz reflection spectra were measured by the THz time-domain system. By attaching an ultra-thin polyimide (10 m) film to the MHA, an obvious blue-shift of reflective resonance peak was observed, which indicated a high sensitivity of MHA to low refractive index materials. This characteristic allows us to achieve MHA-based high-sensitive sensor at THz band.
2013,
25: 1483-1488.
doi: 10.3788/HPLPB20132506.1483
Abstract:
Based on our previous work which introduced an explicit method to design the slow wave circuit of a 0.14 THz broadband folded waveguide traveling wave tube, a 0.14 THz watt-level folded waveguide traveling wave tube has been designed, with a set of slow wave structure parameters determined by analyzing the influence of structure dimensions on its cold characteristics using CST MWS. Over 6 W output power is attained with 3D PIC method by means of CST PS, at around 0.14 THz, as the input power is 20 mW. A transmission tube was fabricated in order to verify the designed electron-optical system. Measurement results show an over 80% electron transmission rate.
Based on our previous work which introduced an explicit method to design the slow wave circuit of a 0.14 THz broadband folded waveguide traveling wave tube, a 0.14 THz watt-level folded waveguide traveling wave tube has been designed, with a set of slow wave structure parameters determined by analyzing the influence of structure dimensions on its cold characteristics using CST MWS. Over 6 W output power is attained with 3D PIC method by means of CST PS, at around 0.14 THz, as the input power is 20 mW. A transmission tube was fabricated in order to verify the designed electron-optical system. Measurement results show an over 80% electron transmission rate.
2013,
25: 1489-1493.
doi: 10.3788/HPLPB20132506.1489
Abstract:
In order to develop the compact high-power terahertz (THz) source, a 0.22 THz source is designed theoretically by adopting the structure of surface-wave oscillator (SWO). We focus on the influence of the slow-wave structure (SWS) on resonant frequency and optimization of the SWS. Combined with the choose of diode, the particle-in-cell (PIC) simulation is performed for the source. The results show that the optimum structure can work stably and generate a terahertz signal in the condition of a input voltage of 200 kV, a current of 2900 A, and a guiding magnetic field of 5 T. The resonant frequency of the output signal is about 0.22 THz, and the output power reaches 19.5 MW with its efficiency of about 3.3%.
In order to develop the compact high-power terahertz (THz) source, a 0.22 THz source is designed theoretically by adopting the structure of surface-wave oscillator (SWO). We focus on the influence of the slow-wave structure (SWS) on resonant frequency and optimization of the SWS. Combined with the choose of diode, the particle-in-cell (PIC) simulation is performed for the source. The results show that the optimum structure can work stably and generate a terahertz signal in the condition of a input voltage of 200 kV, a current of 2900 A, and a guiding magnetic field of 5 T. The resonant frequency of the output signal is about 0.22 THz, and the output power reaches 19.5 MW with its efficiency of about 3.3%.
2013,
25: 1494-1498.
doi: 10.3788/HPLPB20132506.1494
Abstract:
Field emission from carbon nanotube (CNT) has been simulated by a particle-in-cell (PIC) software at pico-second level. The emission current, current density and focus character of a CNT cathode have been discussed. In a diode configuration, the emission current from cathode reaches 1.85 A/cm2 when the anode voltage is 2 kV. While in a triode configuration, the current reaches 2.3 A/cm2 for a gate voltage of 700 V, and the focus performance of electron beam can be optimized by modifying triode parameters and voltage applied to the electrodes. A diode structure with CNT cathode has been fabricated to verify large-current field emission, a total emission current of 52.1 mA and a current density of 6.6 A/cm2 have been obtained from this diode. It proved that field emission cathode can be applied in terahertz source devices.
Field emission from carbon nanotube (CNT) has been simulated by a particle-in-cell (PIC) software at pico-second level. The emission current, current density and focus character of a CNT cathode have been discussed. In a diode configuration, the emission current from cathode reaches 1.85 A/cm2 when the anode voltage is 2 kV. While in a triode configuration, the current reaches 2.3 A/cm2 for a gate voltage of 700 V, and the focus performance of electron beam can be optimized by modifying triode parameters and voltage applied to the electrodes. A diode structure with CNT cathode has been fabricated to verify large-current field emission, a total emission current of 52.1 mA and a current density of 6.6 A/cm2 have been obtained from this diode. It proved that field emission cathode can be applied in terahertz source devices.
2013,
25: 1499-1503.
doi: 10.3788/HPLPB20132506.1499
Abstract:
The measuring methods and experimental results for the parameters including frequency and power of 0.14 THz high-power terahertz pulse are presented. Characterized by high frequency, high peak power and short pulse duration, the terahertz pulse is experimentally measured in frequency using subharmonic heterodyne method combined with cut-off waveguide method, while the far-field power distribution of the radiation pulse is obtained by integration method of power density in the radiation field, and then the radiation power of the single pulse is presented. The measured results under certain experimental conditions show that the high-power terahertz pulse has a frequency of 0.146 3 THz, a pulse duration of about 1.5 ns, and a power level of not less than 0.5 MW.
The measuring methods and experimental results for the parameters including frequency and power of 0.14 THz high-power terahertz pulse are presented. Characterized by high frequency, high peak power and short pulse duration, the terahertz pulse is experimentally measured in frequency using subharmonic heterodyne method combined with cut-off waveguide method, while the far-field power distribution of the radiation pulse is obtained by integration method of power density in the radiation field, and then the radiation power of the single pulse is presented. The measured results under certain experimental conditions show that the high-power terahertz pulse has a frequency of 0.146 3 THz, a pulse duration of about 1.5 ns, and a power level of not less than 0.5 MW.
2013,
25: 1504-1508.
doi: 10.3788/HPLPB20132506.1504
Abstract:
Time delay effect on optical dipole antennas space power synthesis is analyzed. Utilizing terahertz time-domain spectroscopy, we obtain terahertz time-domain spectrogram of 34, 500 and 1000 m optical dipole antenna separately. The time delay effect on space power synthesis is studied in numerical simulation. The result shows that, in the condition of 60% space power synthesis efficiency, the relatively biggest time delay of two arrays of 34, 500 and 1000 m optical dipole antenna is 350.7, 467.6, 450.9 fs, respectively, that for three arrays is 191.1, 250.5, 267.2 fs, respectively, and that for four arrays is 167, 200.4, 217.1 fs, respectively. The numerical simulation of space power synthesis can provide important basis for physical experiment of optical dipole antenna arrays.
Time delay effect on optical dipole antennas space power synthesis is analyzed. Utilizing terahertz time-domain spectroscopy, we obtain terahertz time-domain spectrogram of 34, 500 and 1000 m optical dipole antenna separately. The time delay effect on space power synthesis is studied in numerical simulation. The result shows that, in the condition of 60% space power synthesis efficiency, the relatively biggest time delay of two arrays of 34, 500 and 1000 m optical dipole antenna is 350.7, 467.6, 450.9 fs, respectively, that for three arrays is 191.1, 250.5, 267.2 fs, respectively, and that for four arrays is 167, 200.4, 217.1 fs, respectively. The numerical simulation of space power synthesis can provide important basis for physical experiment of optical dipole antenna arrays.
2013,
25: 1509-1512.
doi: 10.3788/HPLPB20132506.1509
Abstract:
A large current and a high emission current density from printed carbon nanotube (CNT) are reported. To enhance the field-emission current, a small number of metal nano-particles were added to the CNT paste. The metal nano-particles enhanced the emitters-substrate contact and improved the CNTs adhesion properties. A large current of 68.0 mA is obtained from a cathode area of 1.1 mm2, and the high emission current density is about 6.2 A/cm2. The CNT cathode is applied to field-emission vacuum device prototype successfully. Experiments show that current and current density can meet the requirements for large current field-emission electron devices.
A large current and a high emission current density from printed carbon nanotube (CNT) are reported. To enhance the field-emission current, a small number of metal nano-particles were added to the CNT paste. The metal nano-particles enhanced the emitters-substrate contact and improved the CNTs adhesion properties. A large current of 68.0 mA is obtained from a cathode area of 1.1 mm2, and the high emission current density is about 6.2 A/cm2. The CNT cathode is applied to field-emission vacuum device prototype successfully. Experiments show that current and current density can meet the requirements for large current field-emission electron devices.
2013,
25: 1513-1518.
doi: 10.3788/HPLPB20132506.1513
Abstract:
Based on the rigorous electromagnetic field theory, the rigorous expression of terahertz waves in micro-ring resonators with shape and fishnet structure is given in this paper. With the boundary conditions of electromagnetic field, the enhancement effect of the spatial distribution of terahertz waves in the micro-ring resonator with shape and fishnet structure is analyzed. The numerical results show that the electric field is greater than the magnetic field near the ring resonator metal strips. The electric field near the metal strips is obviously stronger than that in other regions, especially in the opening. The THz electric and magnetic fields in the peak position of electromagnetic field in fishnet structure are symmetry with respect to x. The extremum of the electric field appears in the four up and down corners of the large cross, while the extremum of the magnetic field appears in the upper and lower ends of the small cross. The physical interpretation of these phenomena is also given in the point view of the theory of electromagnetic field transmission lines.
Based on the rigorous electromagnetic field theory, the rigorous expression of terahertz waves in micro-ring resonators with shape and fishnet structure is given in this paper. With the boundary conditions of electromagnetic field, the enhancement effect of the spatial distribution of terahertz waves in the micro-ring resonator with shape and fishnet structure is analyzed. The numerical results show that the electric field is greater than the magnetic field near the ring resonator metal strips. The electric field near the metal strips is obviously stronger than that in other regions, especially in the opening. The THz electric and magnetic fields in the peak position of electromagnetic field in fishnet structure are symmetry with respect to x. The extremum of the electric field appears in the four up and down corners of the large cross, while the extremum of the magnetic field appears in the upper and lower ends of the small cross. The physical interpretation of these phenomena is also given in the point view of the theory of electromagnetic field transmission lines.
2013,
25: 1519-1522.
doi: 10.3788/HPLPB20132506.1519
Abstract:
We show a Josephosn junction terahertz harmonic mixer system, in which the high temperature superconducting (HTS) Josephson junction is set up on a cold figure in the small pulse-tube cryocooler working at the bath temperature of 60 K. We improved the experiments by several methods, such as choosing MgO as the substrate, assembling a well-designed planar logarithm periodic antenna to the junction, and using the quasi-optical system with one silicon hyper-hemispherical lens and two off-axis parabolic mirrors on the optical path. During the measurements, the sample was illuminated by a 623 GHz microwave source, and the Shapiro steps in the IV curves of YBCO/MgO bi-crystal junction were observed. The ultimate harmonic order is 24.
We show a Josephosn junction terahertz harmonic mixer system, in which the high temperature superconducting (HTS) Josephson junction is set up on a cold figure in the small pulse-tube cryocooler working at the bath temperature of 60 K. We improved the experiments by several methods, such as choosing MgO as the substrate, assembling a well-designed planar logarithm periodic antenna to the junction, and using the quasi-optical system with one silicon hyper-hemispherical lens and two off-axis parabolic mirrors on the optical path. During the measurements, the sample was illuminated by a 623 GHz microwave source, and the Shapiro steps in the IV curves of YBCO/MgO bi-crystal junction were observed. The ultimate harmonic order is 24.
2013,
25: 1523-1526.
doi: 10.3788/HPLPB20132506.1523
Abstract:
Low temperature (LT) InGaAs materials were grown by gas source molecular beam epitaxy, and the influence of growth temperature as well as arsenic pressure on InGaAs material properties was studied. The optimized deposition conditions were established with the growth temperature of 300 ℃ and the arsenic pressure of 77.3 kPa. By using the structure of In0.52Al0.48As/In0.53Ga0.47As multiple quantum well and doping with Be into InGaAs layers, the resistance of LT-InGaAs material was increased to 1.632106 /Sq, and the carrier concentration was reduced to 1.0581014 cm-3. X-ray diffraction measurements show that LT-InGaAs multiple quantum wells have perfect crystal quality. This multiple quantum well material doped with Be has high trap density and high resistivity, which is suitable material for THz photoconductive antennas.
Low temperature (LT) InGaAs materials were grown by gas source molecular beam epitaxy, and the influence of growth temperature as well as arsenic pressure on InGaAs material properties was studied. The optimized deposition conditions were established with the growth temperature of 300 ℃ and the arsenic pressure of 77.3 kPa. By using the structure of In0.52Al0.48As/In0.53Ga0.47As multiple quantum well and doping with Be into InGaAs layers, the resistance of LT-InGaAs material was increased to 1.632106 /Sq, and the carrier concentration was reduced to 1.0581014 cm-3. X-ray diffraction measurements show that LT-InGaAs multiple quantum wells have perfect crystal quality. This multiple quantum well material doped with Be has high trap density and high resistivity, which is suitable material for THz photoconductive antennas.
2013,
25: 1527-1529.
doi: 10.3788/HPLPB20132506.1527
Abstract:
Tolerance analysis of a filter with different cavity widths is presented, showing that different widths should be used for filters in different frequency bands in order to degrade manufacturing tolerance. Moreover, the effect of various resonant modes is also analyzed. It is found that in terahertz, the cavity length of TE101 mode is smaller than the width of the cavity, and in this case higher resonant modes should be used to increase the Q factor and degrade the tolerance of manufacturing. A 4th order 0.34 THz band pass filter is illustrated. Its measurement shows that the minimum loss is -0.73 dB and all loss is within -2 dB in the frequency range of 0.335 THz to 0.349 THz.
Tolerance analysis of a filter with different cavity widths is presented, showing that different widths should be used for filters in different frequency bands in order to degrade manufacturing tolerance. Moreover, the effect of various resonant modes is also analyzed. It is found that in terahertz, the cavity length of TE101 mode is smaller than the width of the cavity, and in this case higher resonant modes should be used to increase the Q factor and degrade the tolerance of manufacturing. A 4th order 0.34 THz band pass filter is illustrated. Its measurement shows that the minimum loss is -0.73 dB and all loss is within -2 dB in the frequency range of 0.335 THz to 0.349 THz.
2013,
25: 1530-1534.
doi: 10.3788/HPLPB20132506.1530
Abstract:
This article presents a 0.34 THz T/R front-end based on Schottky barrier diode (SBD) techniques. It is designed as a superheterodyne structure, and consists of 0.34 THz sub-harmonic mixer, 0.17 THz X8 multiplier chain and bias circuit. The 0.34 THz sub-harmonic mixer based on anti-parallel diodes is used to transmit and detect the THz signal. The 0.17 THz X8 multiplier chain is cascaded by three doublers and driven amplifiers, which could generate 0.16-0.18 THz local oscillation (LO) signal from 20-22.5 GHz with output power of 5-10 dBm. Experimental measurement indicates the maximum output power of 0.34 THz front end is -14.58 dBm, the lowest single-sideband (SSB) conversion loss is 10.0 dB, and 3 dB intermediate frequency (IF) bandwidth is about 30 GHz. Limited by measurement instruments, the double-sideband (DSB) noise temperature has not been measured, but the calculated value is below 1000 K. The 0.34 THz communication with 16QAM high order modulation has been realized with this front-end, and the data rate is 3 Gb/s.
This article presents a 0.34 THz T/R front-end based on Schottky barrier diode (SBD) techniques. It is designed as a superheterodyne structure, and consists of 0.34 THz sub-harmonic mixer, 0.17 THz X8 multiplier chain and bias circuit. The 0.34 THz sub-harmonic mixer based on anti-parallel diodes is used to transmit and detect the THz signal. The 0.17 THz X8 multiplier chain is cascaded by three doublers and driven amplifiers, which could generate 0.16-0.18 THz local oscillation (LO) signal from 20-22.5 GHz with output power of 5-10 dBm. Experimental measurement indicates the maximum output power of 0.34 THz front end is -14.58 dBm, the lowest single-sideband (SSB) conversion loss is 10.0 dB, and 3 dB intermediate frequency (IF) bandwidth is about 30 GHz. Limited by measurement instruments, the double-sideband (DSB) noise temperature has not been measured, but the calculated value is below 1000 K. The 0.34 THz communication with 16QAM high order modulation has been realized with this front-end, and the data rate is 3 Gb/s.
2013,
25: 1535-1540.
doi: 10.3788/HPLPB20132506.1535
Abstract:
The quasi-optical feed system is a key component of the millimeter/sub-millimeter sensor. The design theory and methods of millimeter/sub-millimeter wave quasi-optical system are described. The varieties, functions and design process of quasi-optical passive devices are generalized. Then, the quasi-optical feed systems, which can realize the dual-polarized receiving and dual-mode composite operation, are constructed and the working principles are also given in detail. Ultimately, the corresponding millimeter-wave dual-reflector antenna is obtained through simulation and optimization, and the whole system with subreflector fixed and main reflector scanning is able to realize 10airspace coverage.
The quasi-optical feed system is a key component of the millimeter/sub-millimeter sensor. The design theory and methods of millimeter/sub-millimeter wave quasi-optical system are described. The varieties, functions and design process of quasi-optical passive devices are generalized. Then, the quasi-optical feed systems, which can realize the dual-polarized receiving and dual-mode composite operation, are constructed and the working principles are also given in detail. Ultimately, the corresponding millimeter-wave dual-reflector antenna is obtained through simulation and optimization, and the whole system with subreflector fixed and main reflector scanning is able to realize 10airspace coverage.
2013,
25: 1541-1544.
doi: 10.3788/HPLPB20132506.1541
Abstract:
This paper reviews three kinds of terahertz (THz) radar cross section (RCS) measurement technologies, viz. microwave up-conversion, laser down-conversion and terahertz time-domain spectrum. Their characteristics like set-ups, specialties and applications are mainly introduced. We build a THz RCS measurement system with solid state components based on microwave up-conversion technology, and employ time-domain method based on the sweep and inverse synthetic aperture radar (ISAR) technologies to perform angle- and frequency-resolved RCS measurements on scale-model targets, then the 2D scattering image and RCS on targets are obtained.
This paper reviews three kinds of terahertz (THz) radar cross section (RCS) measurement technologies, viz. microwave up-conversion, laser down-conversion and terahertz time-domain spectrum. Their characteristics like set-ups, specialties and applications are mainly introduced. We build a THz RCS measurement system with solid state components based on microwave up-conversion technology, and employ time-domain method based on the sweep and inverse synthetic aperture radar (ISAR) technologies to perform angle- and frequency-resolved RCS measurements on scale-model targets, then the 2D scattering image and RCS on targets are obtained.
2013,
25: 1545-1548.
doi: 10.3788/HPLPB20132506.1545
Abstract:
A three-dimensional (3-D) image reconstruction algorithm based on mixed-domain is developed for terahertz holographic imager. Matched filtering in the spatial wave-number domain is employed to focus images in the vertical direction. Combined with back-projection technique used in the other two directions, the algorithm can focus images perfectly without complex 3-D Stolt interpolation computation compared with the frequency-wavenumber algorithm. Besides, motion compensations in the horizontal and range directions get easier to handle. The computational cost of the proposed algorithm is lower than the traditional 3-D back-projection algorithm owing to the FFT-based reconstruction in the vertical direction. Finally, some simulation and experimental imaging results are given in the 0.2 THz band to validate the algorithm.
A three-dimensional (3-D) image reconstruction algorithm based on mixed-domain is developed for terahertz holographic imager. Matched filtering in the spatial wave-number domain is employed to focus images in the vertical direction. Combined with back-projection technique used in the other two directions, the algorithm can focus images perfectly without complex 3-D Stolt interpolation computation compared with the frequency-wavenumber algorithm. Besides, motion compensations in the horizontal and range directions get easier to handle. The computational cost of the proposed algorithm is lower than the traditional 3-D back-projection algorithm owing to the FFT-based reconstruction in the vertical direction. Finally, some simulation and experimental imaging results are given in the 0.2 THz band to validate the algorithm.
2013,
25: 1549-1554.
doi: 10.3788/HPLPB20132506.1549
Abstract:
Detailed components on conductor surface such as micro-structure and roughness will affect the electromagnetic scattering behavior of target in terahertz regime. For weighting this impact, the effect of different surface micro-structure on the electromagnetic scattering of terahertz waves from cylindrical objects is studied, as well as its exhibited law in image domain. First of all, multi-angle and multi-frequency scattered fields are derived for polished, surface-defect, and periodic rough cylinders through the use of the high frequency methods in computational electromagnetics. Then, target images are reconstructed using the rotating target imaging algorithm. The corresponding reconstruction images show that surface structures of micron scale still exhibit notable impact on terahertz radar image results. It implies that terahertz radar can attain more fine information about targets, which will supply new characteristics and technical support for target detection and recognition.
Detailed components on conductor surface such as micro-structure and roughness will affect the electromagnetic scattering behavior of target in terahertz regime. For weighting this impact, the effect of different surface micro-structure on the electromagnetic scattering of terahertz waves from cylindrical objects is studied, as well as its exhibited law in image domain. First of all, multi-angle and multi-frequency scattered fields are derived for polished, surface-defect, and periodic rough cylinders through the use of the high frequency methods in computational electromagnetics. Then, target images are reconstructed using the rotating target imaging algorithm. The corresponding reconstruction images show that surface structures of micron scale still exhibit notable impact on terahertz radar image results. It implies that terahertz radar can attain more fine information about targets, which will supply new characteristics and technical support for target detection and recognition.
2013,
25: 1555-1560.
doi: 10.3788/HPLPB20132506.1555
Abstract:
The paper points out terahertz imaging algorithm has yet to be developed, in contrast to other matured imaging algorithm. It may be said that there is a terahertz gap in the field of imaging algorithm. Then, based on the classification of terahertz imaging, the relationship between radar imaging and terahertz imaging is discussed. The terahertz radar target signature is studied, and the ultimate imaging resolution of different terahertz sources is analysed. Finally, a review of terahertz radar signal processing and imaging algorithm is presented.
The paper points out terahertz imaging algorithm has yet to be developed, in contrast to other matured imaging algorithm. It may be said that there is a terahertz gap in the field of imaging algorithm. Then, based on the classification of terahertz imaging, the relationship between radar imaging and terahertz imaging is discussed. The terahertz radar target signature is studied, and the ultimate imaging resolution of different terahertz sources is analysed. Finally, a review of terahertz radar signal processing and imaging algorithm is presented.
2013,
25: 1561-1565.
doi: 10.3788/HPLPB20132506.1561
Abstract:
In order to design an optical imaging system working in the terahertz range, a comprehensive analysis and comparison of various optical imaging systems are given, the character and unique advantages of off-axis three-mirror system are presented. With the principle, design methods and procedures of off-axis three-mirror system are analyzed, and simple ZEMAX programming language (ZPL) macros are created. Both the pupil and field of view are off-axis properly after optimization with ZEMAX software. Finally, an off-axis three-mirror system working in the terahertz range is designed with a pupil of 250 mm, the IFOV (instantaneous field of view) of 1 mrad, a focal length of 800 mm, and an F number of 3.2. Thus, the off-axis three-mirror quasi-optical system working in the terahertz range is realized.
In order to design an optical imaging system working in the terahertz range, a comprehensive analysis and comparison of various optical imaging systems are given, the character and unique advantages of off-axis three-mirror system are presented. With the principle, design methods and procedures of off-axis three-mirror system are analyzed, and simple ZEMAX programming language (ZPL) macros are created. Both the pupil and field of view are off-axis properly after optimization with ZEMAX software. Finally, an off-axis three-mirror system working in the terahertz range is designed with a pupil of 250 mm, the IFOV (instantaneous field of view) of 1 mrad, a focal length of 800 mm, and an F number of 3.2. Thus, the off-axis three-mirror quasi-optical system working in the terahertz range is realized.
2013,
25: 1566-1568.
doi: 10.3788/HPLPB20132506.1566
Abstract:
To explore the characteristics of terahertz absorption spectra of lipid macromolecules, terahertz time-domain spectroscopy (THz-TDS) is applied to seven types of plant oils and two types of blend oils. The oils are measured in the frequency range extending from 0 to 80 wavenumbers. The absorption features of the oils are different in such a frequency range, indicating that THz-TDS can be used to distinguish different types of oils, which is the basis for analyzing oil composition and distinguishing oil mixtures with THz spectroscopy.
To explore the characteristics of terahertz absorption spectra of lipid macromolecules, terahertz time-domain spectroscopy (THz-TDS) is applied to seven types of plant oils and two types of blend oils. The oils are measured in the frequency range extending from 0 to 80 wavenumbers. The absorption features of the oils are different in such a frequency range, indicating that THz-TDS can be used to distinguish different types of oils, which is the basis for analyzing oil composition and distinguishing oil mixtures with THz spectroscopy.
2013,
25: 1569-1572.
doi: 10.3788/HPLPB20132506.1569
Abstract:
Antimony doped tin oxide (ATO) powder was prepared by liquid phase chemical coprecipitation method with the SnCl45H2O and SbCl3 used as raw materials. The effects of the doping concentration of Sb on the energy gap, and the transmission characteristics in 0.2-1.6 THz were investigated. In particular, the THz time-domain and frequency-domain spectra, the absorption and shielding effect of the ATO were measured. The results indicate that, the energy gap of the ATO decreases first but then increases with the increase of the Sb doping amount. The same tendency emerges in the change of the THz absorption and shielding effect. In the 1.24-1.60 THz range, the ATO with a Sb doping amount of 9% exhibits the highest shielding efficiency of about 45 dB.
Antimony doped tin oxide (ATO) powder was prepared by liquid phase chemical coprecipitation method with the SnCl45H2O and SbCl3 used as raw materials. The effects of the doping concentration of Sb on the energy gap, and the transmission characteristics in 0.2-1.6 THz were investigated. In particular, the THz time-domain and frequency-domain spectra, the absorption and shielding effect of the ATO were measured. The results indicate that, the energy gap of the ATO decreases first but then increases with the increase of the Sb doping amount. The same tendency emerges in the change of the THz absorption and shielding effect. In the 1.24-1.60 THz range, the ATO with a Sb doping amount of 9% exhibits the highest shielding efficiency of about 45 dB.
2013,
25: 1573-1576.
doi: 10.3788/HPLPB20132506.1573
Abstract:
The paper focuses on experiments and testing researches on the attenuation of THz electromagnetic radiation due to atmospheres absorption. The difference system with double light paths is designed to minimize systemic errors caused by the instability of THz radiation sources output power, and to measure changes of transmission power at multiple THz frequency points in the simulated atmospheric environment, so as to explore the law of attenuation of THz waves in different frequency bands. Moreover, a dynamic database of the characteristics of THz atmospheric transmission is established to analyze abundant atmospheric data and provide support for experimental data processing and theoretical research.
The paper focuses on experiments and testing researches on the attenuation of THz electromagnetic radiation due to atmospheres absorption. The difference system with double light paths is designed to minimize systemic errors caused by the instability of THz radiation sources output power, and to measure changes of transmission power at multiple THz frequency points in the simulated atmospheric environment, so as to explore the law of attenuation of THz waves in different frequency bands. Moreover, a dynamic database of the characteristics of THz atmospheric transmission is established to analyze abundant atmospheric data and provide support for experimental data processing and theoretical research.
2013,
25: 1577-1581.
doi: 10.3788/HPLPB20132506.1577
Abstract:
A real-time signal processing system was designed for the 0.14 THz high resolution imaging radar. The hardware structure was established using CPU+GPU+FPGA to enhance its operation ability. In this inverse synthetic aperture radar (ISAR), the range-Doppler algorithm is used to get higher imaging speed, and L-class Wigner-Ville distribution (LWVD) is adopted to improve the cross-range resolution. An algorithm called Keystone transformation is used to dispose the time domain signal by de-chirp processing, and it eliminates the migration through resolution cell (MTRC) in the target imaging. A method of chirp nonlinearity compensation for the imaging system was also proposed. This signal processing module was applied to a terahertz radar system with 0.14 THz carrier frequency and 5 GHz bandwidth. ISAR images were obtained by using this THz radar system with 3 cm resolution in both range and cross-range profiles, showing the validity of the signal processing method.
A real-time signal processing system was designed for the 0.14 THz high resolution imaging radar. The hardware structure was established using CPU+GPU+FPGA to enhance its operation ability. In this inverse synthetic aperture radar (ISAR), the range-Doppler algorithm is used to get higher imaging speed, and L-class Wigner-Ville distribution (LWVD) is adopted to improve the cross-range resolution. An algorithm called Keystone transformation is used to dispose the time domain signal by de-chirp processing, and it eliminates the migration through resolution cell (MTRC) in the target imaging. A method of chirp nonlinearity compensation for the imaging system was also proposed. This signal processing module was applied to a terahertz radar system with 0.14 THz carrier frequency and 5 GHz bandwidth. ISAR images were obtained by using this THz radar system with 3 cm resolution in both range and cross-range profiles, showing the validity of the signal processing method.
2013,
25: 1582-1586.
doi: 10.3788/HPLPB20132506.1582
Abstract:
In order to verify the feasibility of submillimeter wave radiometer in the terminal guidance, the sky brightness temperature and apparent temperature are calculated. Moreover, the experiments for detecting ground metal and coating stealth targets are carried out. The calculations and experiments show that the radiometer can detect ground metal targets in the cold weather and can not detect it with increasing temperature and humidity. Nevertheless, the radiometer can detect high-temperature coating stealth targets regardless of the weather.
In order to verify the feasibility of submillimeter wave radiometer in the terminal guidance, the sky brightness temperature and apparent temperature are calculated. Moreover, the experiments for detecting ground metal and coating stealth targets are carried out. The calculations and experiments show that the radiometer can detect ground metal targets in the cold weather and can not detect it with increasing temperature and humidity. Nevertheless, the radiometer can detect high-temperature coating stealth targets regardless of the weather.
2013,
25: 1587-1591.
doi: 10.3788/HPLPB20132506.1587
Abstract:
Using look-ahead unwrap, sum relaxation and delay relaxation of relaxed look-ahead technique, we develop a pipelined parallel adaptive CMA blind equalization algorithm. An iterated short convolution based fast parallel FIR filter is used to analyze the implementation structure of the filter part of the proposed parallel adaptive equalizer. Meanwhile, a combined short convolution based parallel adaptive weight update algorithm is used to analyze the implementation structure of the weight update part of the proposed parallel adaptive equalizer. A short convolution based, effective pipelined parallel implementation structure of adaptive CMA blind equalization algorithm is then obtained, and the required relationship of pipelined delays of different modules is achieved. FPGA implementation and simulations of the proposed algorithm are also conducted, and compared with MATLAB simulation.
Using look-ahead unwrap, sum relaxation and delay relaxation of relaxed look-ahead technique, we develop a pipelined parallel adaptive CMA blind equalization algorithm. An iterated short convolution based fast parallel FIR filter is used to analyze the implementation structure of the filter part of the proposed parallel adaptive equalizer. Meanwhile, a combined short convolution based parallel adaptive weight update algorithm is used to analyze the implementation structure of the weight update part of the proposed parallel adaptive equalizer. A short convolution based, effective pipelined parallel implementation structure of adaptive CMA blind equalization algorithm is then obtained, and the required relationship of pipelined delays of different modules is achieved. FPGA implementation and simulations of the proposed algorithm are also conducted, and compared with MATLAB simulation.
2013,
25: 1592-1596.
doi: 10.3788/HPLPB20132506.1592
Abstract:
Using the terahertz imaging technology for its microwave penetration characteristics and high resolution of infrared imaging, a near-field terahertz passive synthetic aperture imaging system is put forward on the basis of the infrared and millimeter wave imaging system. Its realization method is briefly analyzed as follows: a 2-D beam scanning antenna structure is used to realize antenna aperture synthesis, through scanning the two antenna beams to acquire the visibility function, then the terahertz image can be obtained by relevant imaging algorithm; this structure can reduce the complexity of the system and guarantee the imaging system performance at the same time. The performance of this system is analyzed by numerical simulation, and the simulation results show that the system has high spatial resolution. Finally, the feasibility of the imaging system is verified by the process simulation of synthetic aperture imaging.
Using the terahertz imaging technology for its microwave penetration characteristics and high resolution of infrared imaging, a near-field terahertz passive synthetic aperture imaging system is put forward on the basis of the infrared and millimeter wave imaging system. Its realization method is briefly analyzed as follows: a 2-D beam scanning antenna structure is used to realize antenna aperture synthesis, through scanning the two antenna beams to acquire the visibility function, then the terahertz image can be obtained by relevant imaging algorithm; this structure can reduce the complexity of the system and guarantee the imaging system performance at the same time. The performance of this system is analyzed by numerical simulation, and the simulation results show that the system has high spatial resolution. Finally, the feasibility of the imaging system is verified by the process simulation of synthetic aperture imaging.
2013,
25: 1597-1600.
doi: 10.3788/HPLPB20132506.1597
Abstract:
This study puts forward an image segmentation algorithm for passive terahertz images. First of all, the captured original terahertz images are denoised in the preprocessing course. Afterwards, we select the seed regions and the growing criteria by analysis and curve fitting of the gray histogram of the denoised images, and then carry out region growing. Experiment results show that the proposed algorithm is able to extract regions of interest from background effectively, which could help to detect the contrabands hidden under the clothes of the target subjects quickly and accurately, and consequently strengthen the practicability of our imaging system.
This study puts forward an image segmentation algorithm for passive terahertz images. First of all, the captured original terahertz images are denoised in the preprocessing course. Afterwards, we select the seed regions and the growing criteria by analysis and curve fitting of the gray histogram of the denoised images, and then carry out region growing. Experiment results show that the proposed algorithm is able to extract regions of interest from background effectively, which could help to detect the contrabands hidden under the clothes of the target subjects quickly and accurately, and consequently strengthen the practicability of our imaging system.
2013,
25: 1601-1604.
doi: 10.3788/HPLPB20132506.1601
Abstract:
A 0.2 THz stepped frequency radar imaging system with 12 GHz bandwidth which uses inverse synthetic aperture to realize two-dimensional high resolution imagery is proposed and designed. The results of Matlab simulation based on system design parameters show that the THz radar imaging system could realize two-dimensional high resolution imagery of the target, and the horizontal and vertical distance can reach centimeter-level resolution.
A 0.2 THz stepped frequency radar imaging system with 12 GHz bandwidth which uses inverse synthetic aperture to realize two-dimensional high resolution imagery is proposed and designed. The results of Matlab simulation based on system design parameters show that the THz radar imaging system could realize two-dimensional high resolution imagery of the target, and the horizontal and vertical distance can reach centimeter-level resolution.
2013,
25: 1605-1608.
doi: 10.3788/HPLPB20132506.1605
Abstract:
Wide band can be achieved in terahertz (THz) spectrum, so a high resolution terahertz imaging system can be realized according to the radar imaging theory. The stepped THz pulse is obtained by mixing and multiplying the microwave source, and a 220 GHz terahertz active imaging system is designed and developed. The resolution experiments of two reflectors imaging are performed in an anechoic chamber, and the range experiment is done outdoor, which shows that the resolution is up to 4 cm and the range reaches 10 m.
Wide band can be achieved in terahertz (THz) spectrum, so a high resolution terahertz imaging system can be realized according to the radar imaging theory. The stepped THz pulse is obtained by mixing and multiplying the microwave source, and a 220 GHz terahertz active imaging system is designed and developed. The resolution experiments of two reflectors imaging are performed in an anechoic chamber, and the range experiment is done outdoor, which shows that the resolution is up to 4 cm and the range reaches 10 m.
