title: Dual-frequency laser Doppler velocimeter for speckle noise reduction and coherence enhancement.
abstract: We study the characteristics of a dual-frequency laser Doppler velocimeter (DF-LDV) based on an optically injected semiconductor laser. The laser operated in a period-one (P1) dynamical state with two optical frequencies separated by 11.25 GHz is used as the dual-frequency light source. With a microwave beat signal carried by the light, the DF-LDV possesses both the advantages of good directionality, high intensity, and high spatial resolution from the light and low speckle noise and good coherence from the microwave, respectively. By phase-locking the two frequency components with a microwave signal, the coherence of the dual-frequency light source can be further improved and the detection range can be much extended. In this paper, velocity resolutions of the DF-LDV with different amounts of speckle noise and at different detection ranges are experimentally measured and analyzed. Compared with the conventional single-frequency LDV (SF-LDV), the velocity resolution of the DF-LDV is improved by 8 × 10(3) times from 2.5 m/s to 0.31 mm/s for a target with a longitudinal velocity vz = 4 cm/s, a transverse velocity vt = 5 m/s, and at a detection range of 108 m.
authors.affiliation: Institute of Photonics Technologies, Department of Electrical Engineering, National Tsing Hua University, Hsinchu 300, Taiwan.
authors.forename: Chih-Hao
authors.initials: CH
authors.lastname: Cheng
authors.forename: Chia-Wei
authors.initials: CW
authors.lastname: Lee
authors.forename: Tzu-Wei
authors.initials: TW
authors.lastname: Lin
authors.forename: Fan-Yi
authors.initials: FY
authors.lastname: Lin
mesh_terms: D016477:Artifacts; D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D017078:Laser-Doppler Flowmetry / Q000295:instrumentation*; D054023:Lasers, Semiconductor