Static and dynamic characterization of a focused laser differential interferometer

Abstract

A focused laser differential interferometer (FLDI) is experimentally characterized via static and dynamic benchtop testing. The static response is probed using a steady, laminar helium jet, and the dynamic response is investigated using an ultrasonic acoustic beam. In the case of the jet, the refractive index field is independently measured using a Mach-Zehnder interferometer operating simultaneously integrated with FLDI. The experimental data for the static response are compared with numerical simulations of the FLDI based on geometric optics and a ray-tracing algorithm, while the dynamic response is compared with an analytical transfer function derived from the same theory. Close quantitative agreement is found between experiment and theory, validating this approach to modeling FLDI performance. Emphasis is given to quantification of the spatial sensitivity of the system which is a key characteristic of FLDI, especially when applied to hypervelocity ground testing facilities where turbulent flow exists in shear or boundary layers outside the core flow.