Sensitivity Improvement of Laser Microphone Using Self-coupling Effect of Semiconductor Laser

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<p>A laser microphone that uses the self-coupling effect of a semiconductor laser is an optical microphone. It has excellent characteristics, such as a wide and flat frequency characteristic. However, as a laser microphone has a large noise component in its output, the signal-to-noise ratio is low. Therefore, the sensitivity of a laser microphone is not sufficiently high for practical use. In this work, two methods to improve the sensitivity of a laser microphone are proposed. The first method uses a sound collector that collects widespread sound waves on a laser beam. The second method uses a right-angle prism that extends the light path. By using a sound collector, the sensitivity can increase up to nine times and the signal-to-noise ratio increases up to six times. However, the sensitivity decreases for frequencies below 10 kHz, and the directivity has a sharp peak. By using a right-angle prism, the sensitivity increases up to three times and the signal-to-noise ratio increases up to six times. In addition, the sensitivity can be improved while maintaining the wide and flat frequency characteristics and the wide directivity.</p>

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