小型环形激光器中He-Ne气体放电辉光压制的光学方法

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

为解决小型环形激光器输出信号信噪比随腔长减小而下降的问题,研制了一种压制He-Ne气体放电辉光的滤光片。该滤光片的中心波长为632.8nm,入射角为45°,其基片是截止波长为550nm的短波截止红色玻璃,基片前表面镀有19层瞙系结构为{HL2HLHLHLH2LHLHLHLH2LH}的窄带滤光片,后表面镀有4层非规整减反膜。使用离子溅射法和石英晶振膜厚监控方式制备了该滤光片,并对其进行了反向工程拟合,拟合的理论曲线与用Lambda950分光光度计正入射实测的透过率曲线较为吻合。将该滤光片胶合在环形激光器的输出镜后表面,其有用的激光信号幅值基本不变,而噪声幅值下降了约80%,表明该滤光片从光学上使输出信号的信噪比提高了5倍,降低了后续电路处理的负担及复杂度,为小型环形激光器的研制起到了一定的作用。

In order to solve the engineering problem of signal-noise-ratio decreasing with smaller optical path length of mini- aturized ring laser, we prepare a narrow band pass filter for suppressing the discharge glow of He-Ne Gas. The filter＇s 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 nm. 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 signaPs amplitude nearly does not change while the noise＇s 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 process- ing circuits and plays a significant role to miniaturized ring laser development.