High Speed Temperature Measurement in Explosive Fireballs Using Tunable Diode Laser Absorption Spectroscopy

Explosively driven flows represent some of the most intense chemical and physical phenomena in a terrestrial setting. They simultaneously incorporate temporally and spatially varying temperature, chemistry, velocity, and almost all other thermodynamic properties. While the surface temperature of large explosive fireballs is readily obtained through emission spectroscopy at a standoff distance, this metric does not characterize the thermodynamics beyond the attenuation length scale¹. Optical depth in small aluminized charges has been measured on the order of a few centimeters and subsiding only after fireball luminosity². Additionally, emission spectroscopy reflects excited state population, which is not always in thermal equilibrium with the ground state³. For these reasons, emission measurements of larger fireballs will likely not be representative of a majority of the event. The work being presented here details the development, testing, and challenges of deploying tunable diode lasers to capture high-speed (30 kHz) absorption temperature and speciation measurements deep inside of explosive fireballs. The diagnostic is used to characterize explosive fireballs generated with different masses of PBXN-5, TNT, and Primasheet® 1000.