We report a simple laser Doppler velocimeter in which the photoacoustic effect was used to measure the rotation wheel speed. A Doppler signal, caused by mixing a returning wave with an originally existing wave inside the CO2 laser cavity, was detected using a microphone in the laser tube. Frequency of the microphone output was in proportion to the rotation speed of a wheel and is dependent on the cosine of the angle between the direction of the laser beam and tangent of wheel velocity. A Doppler-shifted frequency as high as 34kHz was detected using this method. A frequency response of a few megahertz is expected from the laser Doppler velocimeter based on the photoacoustic effect in a CO2 laser by using a wider bandwidth microphone.
Frequency stabilization of a RF excited CO 2 laser on the peak of the Doppler broadened gain curve using the photoacoustic effect generated from the laser itself is achieved. The photoacoustic signal is directly coupled from a RF discharge chamber using a condenser microphone into an amplifier and a lock-in stabilizer. The frequency stability is estimated to be better then 3×10 -8 . I.
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