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UBC Undergraduate Research

Design, construction, and characterization of an interference-filter stabilized external-cavity diode laser Bowden, William; Quentin, Damien; Sun, Jon-Paul


As scientists understand more about the principles of atomic physics, they need tools which allow them to conduct precise measurements which reveal the fundamental properties of the building blocks of matter. One of the most important of these tools is the laser—a coherent light source with well defined frequency—that is capable of exciting and even cooling atoms. In this report we develop techniques for measuring the linewidth and stability of narrow bandwidth interference filter-stabilized external cavity diode lasers. Based on the characterization of two prototypes lasers, we identified key design parameters affecting laser linewidth and stability. Using these results, we designed a monolithic, hermetically sealable, diode laser using the same interference based feedback system. Using characterization techniques found in literature, such as self-heterodyne and heterodyne interference linewidth measurements, we measured an upper limit for the prototype diode laser linewidth of 10 kHz. This is significantly less than the upper limit of 100 kHz defined in the project proposal. We ensured the output was stable and capable of continuous single mode operation using a Fabry–Pérot interferometer. Precise focal lengths of optical components within the cavity were measured using a conventional knife-edge technique. The effects of misalignment on laser performance were investigated to provide reasonable tolerances for machining and adjustment ranges of components. The optical transmission of a commercial and a custom manufactured interference filter were characterized using variable angle transmission tests. This data was used to determine the tuning range and precision of the optical filters within the cavity to achieve the desired frequency range and sensitivity of hundreds of GHz and 1 GHz respectively. We have demonstrated that the desired performance characteristics can be achieved using interference filter-stabilized diode lasers. Therefore, we recommend a more robust laser should be fabricated whose design is outlined and justified in this report. This monolithic design will have improved stability and increased sensitivity to frequency tuning. This device must be characterized using the methods developed when testing the prototype lasers to ensure it meets its performance specifications. We outline issues with these testing methods and explain why we believe a conventional heterodyne measurement using two lasers would provide more accurate results than the self-heterodyne measurement. However, this will require the implementation of a control system to lock the lasers together to limit drifting of the beat frequency. This drifting is currently preventing accurate linewidth measurements. After completion of the above mentioned experiments and performance goals for the laser are met, multiple laser units can be manufactured for general use for atomic physics applications.

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