Abstract
Krypton (Kr)-based tagging velocimetry is demonstrated in a ${\rm Kr}/{\rm N}_2$ jet at 100 kHz repetition rate using a custom-built burst-mode laser and optical parametric oscillator (OPO) system. At this repetition rate, the wavelength-tunable, narrow linewidth laser platform can generate up to 7 mJ/pulse at resonant Kr two-photon-excitation wavelengths. Following a comprehensive study, we have identified the 212.56 nm two-photon-excitation transition as ideal for efficient Kr-based velocimetry, producing a long-lived ($\sim\!{40}\;\unicode{x00B5} {\rm s}$) fluorescence signal from single-laser-pulse tagging that is readily amenable to velocity tracking without the need for a second “read” laser pulse. This long-lived fluorescence signal is found to emanate from ${\rm N}_2$—rather than from Kr—following efficient energy transfer. Successful flow velocity tracking is demonstrated at multiple locations in a high-speed ${\rm Kr}/{\rm N}_2$ jet flow. The 100 kHz repetition rate provides the ability to perform time-resolved velocimetry measurements in high-speed and even hypersonic flow environments, where standard velocimetry approaches are insufficient to capture the relevant dynamics.
© 2021 Optical Society of America
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