Frequency Stabilization of Semiconductor Laser for Optical Metrology

对可见光半导体激光器光谱宽度的测量进行了实验研究，目的是将半导体激光器的频率稳定在分子的吸收线上.研究了670 nm半导体激光器在光反馈作用下的振荡模式行为。为了滤除激光器多模输出的单频峰，研制了一种结构简单的法布里-珀罗标准具。它表现出良好的旁瓣衰减.研制了一台扫描迈克尔逊干涉仪，用于测量可见度随光程差的变化。所得曲线可用于计算半导体激光器的光程，并可用于分析振荡模式.本文研究了He-Ne激光器633 nm光束在调制频率为50和100 MHz时的光学相位调制，用光学拍频检测法观察到了一个清晰的边带峰。结果表明，由于边带的中心频率可以通过改变调制频率进行扫描，因此边带对于探测分子吸收线是有用的。该系统可用于半导体激光器.为了测量光谱宽度，对两个半导体激光器670 nm光束混合产生的光学拍音进行了检测。尽管对两束激光的光轴和波面进行了精确的对准，并对激光器的振荡频率进行了微调，但没有检测到拍频。这是使激光器稳定在窄分子吸收线上最重要和必要的措施。我们将继续这项实验研究，改进我们的测量系统和脸红我们的实验技术。

Experimental research for measuring spectral width of visible semiconductor lasers has been done, aiming to stabilize frequency of semiconductor laser at an absorption line of a molecule.1. Behavior of oscillation mode of 670nm semiconductor laser, which depends on optical feed back, was investigated. A Frabry-Perot etalon with a simple structure was made for filtering single frequency peak of multimode output of the laser. It shows good attenuation of side lobes.2. A scanning Michelson interferometer was made to measure visibility active as a function of optical path difference. The obtained curve makes possible to calculate optical patil length of the semiconductor laser and also oscillation mode can be analyzed.3. Optical phase modulation of 633nm beam of a He-Ne laser at modulation frequency of 50 and 100MHz was examined and a clear peak of sideband was observed by optical beat detection. The results shows that the sideband will be useful for detecting molecular absorption lines since its central frequency can be swept by changing modulation frequency. This system can be used for the semiconductor laser.4. Detection of optical beat note, which should be generated by mixing 670nm beams of two semiconductor lasers, was done intending to measure the spectral width. In spite of precise alignment of optical axises and wave surface of both beams and fine tuning of the oscillation frequency of the lasers, the beat has not detected. This is the most important and necessary measurement for stabilizing the laser at a narrow molecular absorption line. We will continue this experimental research improving our measuring system and blushing tip our experimental technique.