Laser output power stabilization for circular laser writing systems by using acousto-optic modulator

We present experimental results on the output power stabilization of an Ar+ laser for a direct circular laser writing system (CLWS). Instability of the laser output power in the CLWS causes resolution fluctuations of being fabricated diffractive optical elements or computer-generated holograms. For the purpose of reducing the power fluctuations, we have constituted a feedback loop with an acousto-optic modulator, a photodetector, and a servo controller. Here very important things are proper conception of the servo controller and selection of a proper photodetector depending on what kinds of lasers to be controlled. In this system, we have achieved the stability of ± 0.20 % for 12 minutes and the relative intensity noise level of 2.1 x 10-7 Hz-1/2 at 100 Hz. In addition, we applied our system to a 2 mW internal mirror He-Ne laser. As a consequence, we achieved the output power stability of ± 0.12 % for 25 minutes.

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