Simultaneous Laser Absorption Spectroscopy Measurements of Temperature, CO, and CO2 at Near-MHz Repetition Rates in Post-Detonation Fireballs of PETN

Laser absorption spectroscopy was used to obtain measurements of temperature, CO, and CO2 in post-detonation fireballs of 12 mm diameter hemispherical charges of pentaerythritol tetranitrate (PETN). A quantum-cascade laser (QCL) emitting near 2008.5 cm−1 was used to measure absorbance spectra of CO, while an interband-cascade laser (ICL) emitting near 2394.75 cm−1 was used to measure absorbance spectra of CO2. The QCL frequency was tuned across three CO transitions with a 1 MHz sawtooth waveform, while the ICL frequency was tuned across one CO2 transition with a 500 kHz square wave. The measurements were acquired simultaneously on a single line-of-sight located 167 mm from the PETN hemisphere. A least- squares fitting routine was used to infer temperature, pressure, and species column pressures (PCOL and PCO2L) from the measured absorbance spectra. This work presents the first simultaneous measurements of CO and CO2 in post-detonation fireballs of energetic materials, thereby demonstrating the potential of mid-IR LAS to provide high-rate characterization of carbon oxidation in these environments.