Frequency Stabilization of Semiconductor Laser for Optical Metrology

为了将半导体激光器的频率稳定在分子的一条吸收线上，进行了可见半导体激光器光谱宽度测量的实验研究。研究了670 nm半导体激光器的振荡模式与光反馈的关系。制作了一种结构简单的Frabry-Perot标准具，用于滤除激光器多模输出的单频峰值。显示出良好的旁瓣衰减特性。制作了一台迈克尔逊扫描干涉仪，用于测量能见度随光程差的变化。得到的曲线为计算半导体激光器的光学帕蒂尔长度和分析振荡模式提供了可能。对He-Ne激光器633 nm光束在50 MHz和100 MHz调制频率下的光学相位调制进行了研究，通过光学拍频检测，观察到了清晰的边带峰值。结果表明，由于边带中心频率可通过改变调制频率而被扫频，因此该边带可用于分子吸收线的探测。该系统可用于半导体激光器。为了测量光谱宽度，对由两个半导体激光器的670 nm光束混合产生的光学拍频音符进行了检测。尽管对两束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。这是将激光器稳定在窄分子吸收线上最重要、最必要的措施。我们将继续这项实验研究，改进我们的测量系统，并脸红提示我们的实验技术。

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.