Megahertz-rate NO planar laser-induced fluorescence of reacting flows using tunable 5th harmonic Nd:YAG with A-X and B-X excitation

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Abstract
This article presents, to the best of our knowledge, the first demonstration of burst-mode nitric oxide (NO) planar laser-induced fluorescence measurement of a reacting environment via Nd:YAG 5th harmonic excitation. A tunable pulse-burst laser generated 1 ms bursts of resonant 213 nm radiation at 200 kHz, 500 kHz, and 1 MHz repetition rates with 16 mJ, 3.5 mJ, and 0.35 mJ average pulse energies, respectively. Nitric oxide, naturally formed in the vicinity of an oxy-acetylene flame, was targeted via three excitation schemes: γ(1, 0), γ(1, 0) + β(5, 1), and β(4, 1). The generated fluorescence was collected in two separate spectral windows to demonstrate the selectivity of the electronic excitation and explore new filtering approaches for high background luminosity environments: 240 nm–260 nm and 275 nm–375 nm. Overall, this new method of UV-light generation for NO excitation performed very well with a substantial amount of collected signal even with modest energy levels accessible at a 1 MHz rate. The primary advantage of utilizing the 5th harmonic to access NO resonances was its simplicity and robustness through direct burst mode laser up-conversion and simplified master oscillator, power amplified (MOPA) frequency control, obviating the need for an optical parametric oscillator.
Funding Information
  • Office of Naval Research (N00014-23-1-2458)

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