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

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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.