Burst-mode femtosecond laser electronic excitation tagging for kHz-MHz seedless velocimetry

摘要

Burst-mode femtosecond laser electronic excitation tagging (FLEET) of nitrogen is introduced for tracking the velocity field in high-speed flows at kilohertz-megahertz (kHz-MHz) repetition rates without the use of added tracers. A custom-built Nd:glass femtosecond laser is used to produce 500 pulses per burst with pulses having a temporal separation as short as 1 mu s, an energy of 120 mu J, and a duration of 274 fs. This enables 2 orders of magnitude higher measurement bandwidth over conventional kHz-rate FLEET velocimetry. Characteristics of the optical system are described, along with a demonstration of time-resolved velocity measurements with similar to 0.5% precision in a supersonic slot jet. (C) 2020 Optical Society of America