High-repetition-rate interferometric Rayleigh scattering for flow-velocity measurements
High-repetition-rate interferometric-Rayleigh-scattering (IRS) velocimetry is demonstrated for non-intrusive, high-speed flow-velocity measurements. High temporal resolution is obtained with a quasi-continuous burst-mode laser that is capable of operating at 10–100 kHz, providing 10-ms bursts with pulse widths of 5–1000 ns and pulse energy > 100 mJ at 532 nm. Coupled with a high-speed camera system, the IRS method is based on imaging the flow field through an etalon with 8-GHz free spectral range and capturing the Doppler shift of the Rayleigh-scattered light from the flow at multiple points having constructive interference. The seed-laser linewidth permits a laser linewidth of < 150 MHz at 532 nm. The technique is demonstrated in a high-speed jet, and high-repetition-rate image sequences are shown.
The authors thank Drs. Jayanta Panda and Amy Fagan of NASA for many helpful discussions. Dr. Jordi Estevadeordal acknowledges the AFRL Summer Faculty Fellowship Program and North Dakota State University support. Approved for public release; distribution unlimited (# 88ABW-2017-0533).
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