| Summary: | 碩士 === 國立清華大學 === 光電工程研究所 === 99 === In this research, we successfully developed a dual-frequency Laser Doppler Velocimeter (LDV) based on an optically injected semiconductor laser. With the advantages of high coherence, high power, and low divergence angle, the LDV has long detection range, good precision and accuracy, and great target selection ability. However, with a wavelength in the micrometer range, the LDV is very sensitive to the atmosphere noise and the surface nature of the detection targets. For objects that have surface roughnesses larger than the wavelength of the emitting laser, the speckle effect will be induced and the bandwidth of the detection signal will be broadened. Under such circumstance, the accuracy and resolution in velocity measurement will be degraded. Therefore, we proposed and developed a dual-frequency LDV based on the nonlinear dynamics of semiconductor lasers to mitigate the speckle effect. Three major achievements have been realized in this study: (1) developing the dual-frequency LDV based on the nonlinear dynamics of semiconductor lasers, (2) demonstrating velocity measurement in a velocity range of 1 cm/s to 100 cm/s with an accuracy smaller than 1.2 %, and (3) comparing the dual-frequency LDV with a single-frequency LDV to show its ability in suppressing the speckle effect.
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