Birefringent dual-frequency laser Doppler velocimeter using a low-frequency lock-in amplifier technique for high-resolution measurements

A birefringent dual-frequency laser with a half-intracavity has been used to develop a laser Doppler velocimeter (LDV). The developed LDV utilizes a new signal-processing method based on a lock-in amplifier to achieve high-resolution velocity measurements and the discrimination of positive and negative velocities. Theoretical analysis and simulation results are presented. The velocity measurement experiments by using a high-precision linear stage are performed to verify the performance of the LDV. Compared with the previous dual-frequency LDVs, the average velocity resolution of the developed LDV is improved from 0.31 mm/s to 0.028 mm/s for a target without the rotational velocity. The measurement results show that our new technique can offer a powerful instrument for metrology sciences.