Colinear focused laser differential interferometry and self-aligned focusing schlieren

Abstract

A colinear focused laser differential interferometer (FLDI) and self-aligned focusing schlieren (SAFS) system has been assembled and tested in the laboratory, using a turbulent jet of compressed air issuing from a small needle nozzle to provide a high frequency density object. Measurements verified that the coupling of the SAFS system onto the optical axis of the FLDI system had negligible influence on the FLDI system’s data, including tests that assessed the influence of the inclusion of dichroic mirrors, dichroic mirror reflection angle, dichroic mirror positioning relative to the Wollaston prisms of the FLDI system, and SAFS light propagation direction. A qualitative comparison of the focusing ability of the two systems was made, and FLDI power spectral density estimates and SAFS spectral proper orthogonal decomposition were used for quantitative comparisons of the acoustic frequency of the jet, with good agreement between the two. The success of the system integration and resulting jet testing demonstrates the utility of this colinear, simultaneous FLDI/SAFS measurement system.