Long Xingwu

629 nm He-Ne Laser Using Built-in Fabry-Perot Etalon

He-Ne激光器采用内置法布里-珀罗（F-P）标准具的方法可以获得与633 nm 紧邻的629 nm谱线，这是用传统的镀膜方法无法实现的。分析了由于激光腔内的温度变化引起的629 nm谱线透射窗口的移动。为了得到稳定的629 nm波长输出，估算了F-P标准具的角度调节范围下限。提出了一种大角度范围的压电角度调节机构，应用于F-P标准具的角度调节。同时采用反馈控制算法实现了629 nm波长的稳定输出，稳定输出功率约80 μW。

Multi-Wavelength Conversion Based on Single Wavelength Results in Phase Retardation Measurement

We introduce an instrument for single wavelength measurement of phase retardation based on the laser feedback phenomenon. A method of multi-wavelength conversion for this instrument is proposed and the conversion results are analyzed. System calibration is used to eliminate the conversion error. The experimental results show that the maximum error after conversion is 0.26°. Through the present work, the application of laser feedback instrument for single wavelength measurement of a wave plate is expanded to the multi-wavelength range. This will expand the application area of the instruments.

Note: Laser Doppler velocimeter using a dual-longitudinal-mode laser source

This paper presents a new laser Doppler technique using a dual-longitudinal-mode He-Ne laser as the laser source. Theoretical analysis shows that the Doppler frequency is proportional with the frequency difference of the two modes. The Doppler frequency in this technique is very low compared with the one in the single-mode laser Doppler technique. The new laser Doppler technique can be used to measure high speed. Experiment results show that the Doppler frequency is only about 82 Hz while the measurement speed reaches 31.4 m∕s. The signal-to-noise ratio of the Doppler signal is improved by the technique of digital filter and digital autocorrelation.