Post-Incident Shock Wave Measurements of Gas Properties at 1 MHz Using Scanned-Wavelength-Modulation Spectroscopy

This study demonstrates a laser absorption spectroscopy sensor using the scanned-wavelength-modulation spectroscopy (scanned-WMS) technique to measure gas properties post-incident shock waves at a measurement rate of 1 MHz. The sensor employs near-infrared \(\mathrm{H_2O}\) transitions to infer temperature, pressure, and species concentration from the WMS-2f/1f and WMS-4f/2f harmonic signals. To enable accurate measurements, a novel method is introduced for determining the relative phase shift between the intensity and wavelength of the laser at MHz modulation frequencies. This method is independent of other laser characterization parameters and does not require knowledge of the environment in which the signals are obtained. Additionally, we discuss several modifications to key hardware used in this study. Gas properties inferred from our measurements were found to be within 3.5% of the expected values when using the known pressure to post-process the data, and were within 5% when utilizing higher-order harmonics demonstrating the sensors accuracy.

Recommended citation: Guerrero, Jose, and Mirko Gamba. "Post-Incident Shock Wave Measurements of Gas Properties at 1 MHz Using Scanned-Wavelength-Modulation Spectroscopy." AIAA SCITECH 2025 Forum. 2025.
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