The effect of spot size on quality factor of Laser Doppler Velocimeter

Abstract

Quality factor is an important evaluation index of Laser Doppler Velocimeter (LDV). In order to study the effect of spot size on quality factor, the effects of signal light intensity and transit time on the quality factor are discussed theoretically. In addition, the distribution of quality factor of LDV was measured and examined. Theoretical analysis and experimental results demonstrate that: Due to the symmetry of Gaussian beam, the distribution of quality factor is symmetric. Furthermore, the light intensity of Doppler signal at the waist spot of Gaussian beam is the largest while the transit time of moving particles diminishes due to the decrease of spot diameter, causing spectrum leakage. Under the influence of both Doppler signal intensity and transit time, the distribution of quality factor appears concave phenomenon.