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Measurement of supersonic jet screech with focused laser differential interferometry.

Focused laser differential interferometry (FLDI) is used to measure a well-characterized, 17 kHz screech tone emitted from an underexpanded Mach 1.5 jet. Measurements are made at numerous spatial locations in and around the jet flow-field, where intrusive diagnostics would otherwise influence the flow-field. Results from FLDI measurements are shown to agree with measurements from microphones and analyses of high-speed schlieren. The agreement is used to demonstrate FLDI is a valid and accurate technique for measuring screech tones in jet flow-fields, and furthermore that FLDI can be used to measure jet screech at various spatial locations around the jet, and notably inside of the jet, where microphones and other intrusive diagnostics cannot be used effectively.