Laser Doppler cross-sectional velocity distribution measurement combining 16-channel spatial encoding and non-mechanical scanning

•The LDV combines non-mechanical scanning and simultaneous multipoint measurement.•Multichannel serrodyne frequency shifting is used for spatial encoding.•An asymmetrical push-pull configuration is introduced to realize a 16-channel system.•Two-dimensional velocity distribution was successfully measured.

This paper presents a differential laser Doppler velocimeter (LDV) for measuring the velocity distribution on a two-dimensional cross section. The author has proposed the LDV that combines non-mechanical scanning and simultaneous multipoint measurement using spatial encoding. In this paper, this method is expanded to a 16-channel system that facilitates more dense two-dimensional cross-sectional velocity distribution measurements. The spatially encoded measurement points aligned in the transverse direction are generated and scanned in the axial direction in a non-mechanical manner using diffraction gratings and a tunable laser. Multichannel serrodyne frequency shifting using a LiNbO3 phase-shifter array is used to generate spatially encoded points with a simple structure. An asymmetrical push-pull configuration is introduced to increase the number of the spatially encoded points. The experimental results indicate that the two-dimensional velocity distribution was successfully measured by the proposed configuration.