Single-shot nitric oxide ionization induced flow tagging and imaging in a cold hypersonic flow using 5th harmonic Nd:YAG laser at 200 kHz

This article presents the first demonstration of the tunable 5th harmonic of a Nd:YAG pulse-burst laser used for single-shot velocity and acceleration measurements via Nitric-oxide ionization induced Flow Tagging and Imaging. This demonstration was performed in a highly transient hypersonic flowfield created by injecting a supersonic jet perpendicularly to the main hypersonic flow in the Actively Controlled Expansion Tunnel at Texas A&M University. Overall, this new method of resonant UV-light excitation leading to the generation of IR and near IR emission for velocimetry purposes performed well, with spatially resolved single-shot velocities measured at 200 kHz at multiple locations. Additionally, the demonstration was successfully completed in a low-enthalpy hypersonic flow with a static temperature of 60 K, suggesting effective 5th harmonic energy coupling despite the low population of high rotational states of nitric oxide at those temperatures via quasi-resonant two-photon ionization.