Development of frequency stabilized, narrow linewidth, continuously tunable semiconductor laser systems

本计画的目标是发展一个频率稳定、窄线宽、连续可调谐的雷射系统，其中半导体雷射被强制以外腔模式振荡。该系统可方便地应用于高分辨率光谱分析和激光冷却系统。为了使反射率最小化，必须精确控制膜的厚度。在镀膜过程中，连续记录激光功率，以尽可能精确地预测最小点。我们构造了一个具有足够机械自由度的外腔系统，以检查每个自由度的灵敏度。通过消除不必要的自由度，我们制作了一个刚性腔系统，通过在腔中安装镀膜激光二极管，我们可以连续调谐激光超过25 nm。作为可调谐性的证明，我们将单个半导体激光器调谐到钾和铷的D线上，激光冷却原子的吸收光谱表明振荡线宽被缩窄到1 MHz以下。建立了外腔半导体激光器的理论模型，并与实验结果进行了比较。

The goal of this project is to develop a frequency stabilized, narrow linewidth, and continuonsly tunable laser system in which a semiconductor laser is forced to oscillate in external cavity modes. The system can conveniently be used in high resolution spectroscopy and laser cooling systems.One of the facets of laser diode is anti-reflection (AR) coated with silicon oxide. In order to minimize the reflectivity, the thickness of the film has to be controlled precisely. In the process of coating, the laser power is continuously recorded to predict the minimum point as precise as possible. With this care, we can produce a laser diode which can be tuned continuously.A external cavity system with enough mechanical degrees of freedom is constructed to check sensitivity of each freedom. We then make a rigid cavity system by eliminating unnecessary freedom.By installing the coated laser diode in the cavity, we can continuously tune the laser over 25 nm. As a demonstration of the tunability, we tune a single laser diode to the D lines of potassium and rubidium.Absorption spectroscopy of laser cooled atoms shows the oscillation linewidth is narrowed down to 1 MHz or below.A theoretical model for the external cavity semiconductor laser is developed and comparison with experimental results is made.