Characterization of a Focused Laser Differential Interferometer

Abstract

A focused laser differential interferometer (FLDI) has been experimentally characterized. The static response was probed using a steady, laminar helium jet, and the dynamic response was investigated using a free ultrasonic acoustic beam. In the case of the jet, the refractive index field was independently measured using a Mach-Zehnder interferometer operating simultaneously alongside FLDI. The experimental data were compared with numerical simulations of the FLDI response based on geometric optics and a ray-tracing algorithm. Close quantitative agreement was found between data and simulation results, validating this approach to modeling FLDI performance. Emphasis was given to quantification of the spatial sensitivity of the system, a key characteristic of FLDI, especially when applied to hypersonic ground testing facilities where strong turbulent flow exists outside the core flow.

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