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A Sensitive Fiber-Optic Gas Spectrophone

An improved spectrophone for measurements of laser absorption in gases has been tested. The device employs a fiber-optic interferometer, wound into a cylindrical shape, as the acoustic sensor. Performance of the device was evaluated by measuring the absorption of 3.39 μm HeNe laser radiation in a calibrated mixture of methane in Argon. Results indicate a minimum detectable absorption capability of 2x10-7cm-1 W/√ MHz , although a background signal 30 dBV above the noise limited performance. We report an improvement in sensitivity several orders of magnitude above the first fiber-optic spectrophone.