Mach-Zehnder interferometric filter based planar Doppler velocimetry (MZI-PDV)

This paper describes the development of a Mach-Zehnder interferometric filter based planar Doppler velocimetry (MZI-PDV) flow measurement technique. The technique uses an unbalanced Mach-Zehnder interferometer (MZI) to convert Doppler frequency shifts into intensity variations. The free spectral range of the interferometric filter can be selected by adjusting the optical path difference of the MZI. This allows the velocity measurement range and resolution to be varied. In contrast to molecular filter based PDV any laser source with single-frequency operation and a narrow linewidth can be used as the requirement for a suitable absorption line is no longer necessary. The processing methods used to extract the velocity information are described and discussed. The construction of a MZI-PDV system that incorporates a phase-locking system designed to stabilize the filter is described and example measurements made on the velocity field of a rotating disc and an axis-symmetric air jet are presented.