Broadband second harmonic generation of spatially chirped pulses
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摘要: 提出一种新型的宽带倍频方案，利用时空耦合效应将宽带的时间啁啾光转换成空间啁啾光，采用多块晶体并联、各晶体独立调谐的技术途径对空间啁啾光进行谐波转换，因此倍频效率与窄带激光倍频相当。理论研究表明，采用KDP晶体I类位相匹配，对中心波长为1 053 nm的宽带基频光实现了带宽约30 nm、转换效率大于60%的高效率宽带二倍频。而且倍频光仍为线性啁啾宽带光，具备可压缩性。Abstract: Efficient broadband harmonic conversion has important application value in high power laser. However, it is difficult to achieve broad bandwidth and high efficiency at the same time in the traditional second harmonic generation (SHG). This paper proposes a novel broadband SHG scheme, which uses the space-time coupling effect to transform the temporally chirped pulse into a spatially chirped one, and then several spliced crystals are used to achieve efficient broadband frequency conversion. Simulation results show that for the spliced KDP crystal, the conversion efficiency of the fundamental harmonic reaches about 60%, for pulse bandwidth of 30 nm and central wavelength of 1 053 nm. Moreover, the frequency doubled light is still linear and broadband, and can be compressed as the fundamental pulse.
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Key words:
- second-harmonic conversion /
- broadband light /
- frequency domain /
- spatial chirp /
- temporal chirp
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图 1 基于光栅和棱镜进行展宽的空间啁啾宽带二倍频方案的示意图
Figure 1. Schematic of the broadband second harmonic generation (SHG) with pulse spatially chirped by diffraction grating and dispersing prisms
图 2 空间啁啾倍频方案中，单一晶体和两块晶体拼接的情况下，不同频率成分的转换效率及倍频光的光强曲线
Figure 2. Conversion efficiency of different frequency and the intensityly of the frequency-doubled pulse using a single crystal and two spliced crystals in the spatially chirping scheme
图 3 KDP晶体I型倍频过程中，传统倍频方案、多块晶体并联的空间啁啾倍频方案下，倍频效率随晶体长度的分布曲线
Figure 3. Efficiency changes with crystal length of the traditional SHG and SHG with spatially chirped pulse in the KDP I crystal
图 4 在空间啁啾倍频方案中，输出倍频光的归一化光强度在（a）空间域和（b）频率域上的分布曲线
Figure 4. Normalized intensity of frequency-doubled pulse of spatial (a) and frequency (b) domain
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