Optical method for He-Ne gas’s discharge glow suppression in miniaturized ring laser

In order to solve the engineering problem of signal-noise-ratio decreasing with smaller optical path length of miniaturized ring laser, we prepare a narrow band pass filter for suppressing the discharge glow of He-Ne Gas. The filters central wavelength is 633 nm, and is incident at angle of 45 from the air. The substrate of the filter is a long wave pass red glass with transiting wavelength of 550 m. We deposit a 19-layer filter with layer structure as {HL2HLHLHLH2LHLHLHLH2LH} on one side of the substrate, and a 4-layer non-quart-wave antireflection coating on the other, by method of ion sputtering and quartz crystal monitoring of layer thickness. We measure the transmittance curve of the deposited filter by Lambda950 spectrometer, and find a good fit to it by reverse engineering technique. When this filter is glued to the output mirror of ring laser, the counting signals amplitude nearly does not change while the noises amplitude decreases by 80%. It is showed that a fivefold improvement of signal-noise-ratio has been optically achieved by the filter, which decreases the burden and complexity of the following processing circuits and plays a significant role to miniaturized ring laser development.