Distributed feedback lasers, which feature rapid wavelength tunability, are not presently available in the yellow and orange spectral regions, impeding spectroscopic studies of short-lived species that absorb light in this range. To meet this need, a rapidly tunable laser system was constructed, characterized, and demonstrated for measurements of the NH₂ radical at 597.4 nm. The system consisted of three main parts: (1) a distributed feedback diode laser operating at 1194.8 nm, (2) a fiber-coupled optical amplifier, and (3) a periodically poled lithium niobate (PPLN) waveguide for second-harmonic generation. A phase-matching optical frequency bandwidth of 118 GHz and a second-harmonic generation efficiency of 109%/W were determined for the PPLN waveguide, and the intensity and wavelength stability of the system were measured. The rapid-tuning capabilities of the laser system were characterized to explore its potential for use in scanned-direct absorption and wavelength modulation spectroscopy experiments. The feasibility of scanned-direct absorption up to a scan rate of 900 kHz and wavelength modulation spectroscopy at modulation frequencies up to 800 kHz were demonstrated. Finally, the system was deployed in a series of shock tube experiments in which the concentration of NH₂ radicals was measured during the decomposition of NH₃ behind reflected shock waves.

Quantitative, high-bandwidth measurements of temperature, pressure, and velocity are needed to characterize high-speed flows and validate numerical simulations. To that end, this work demonstrates rapid, multi-parameter spectrally resolved planar laser-induced fluorescence (SR-PLIF) for spatially resolved, calibration-free measurements of these three key quantities using the gamma-bands of nitric oxide near 225.33 nm. The SR-PLIF technique was validated from 295–420 K and 3.48–20.4 kPa using a static gas cell and exhibits an average temperature and pressure error of 2% and 4%, respectively. The diagnostic was then used to study an underexpanded jet at rates up to 1 kHz and a spatial resolution of 220µm, with results showing favorable agreement with numerical simulations.