Frequency stabilization of an internal-mirror He-Ne laser by means of a microprocessor controller.

概要

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Simultaneous stabilization of the amplitude and frequency of a two-mode internal-mirror He-Ne laser (λ=633 nm) using a microprocessor controller is reported. The intensity difference between two orthgonally-polarized axial modes normalized by the total intensity is caluculated as a controlled signal. The cavity length is controlled by manipulating the current of a heater wound around the laser tube according to digital PID or I-PD algorithms so that the controlled signal coincides with a reference signal. By adjusting the reference signal, stabilized laser frequency can be tuned within ±300 MHz around the mean frequency of the atomic resonance frequencies of 20Ne and 22Ne. Frequency stability estimated by the error between the controlled and reference signals is better than 3×10-8 over a period of 30 minutes. Beat frequency fluctuations between two stabiliezed lasers over a 8 minutes are in the range 1×10-8 to 2×10-8 depending on the selected direction of polarization.
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