Acoustic measurements of laser-induced microshocks: time of arrival to yield estimations

Abstract

High-fidelity microphones can be used to characterize laser-generated microblast waves (“microshocks”) in tabletop experiments. This study probes both spherical and hemispherical microshocks, analogous to height-of-burst or surface-burst geometries, at distances of 1–15 cm and laser energies in the range of ~  300–630 mJ under face-on (\(0^{\circ }\)) or side-on (\(90^{\circ }\)) microphone orientations. We take a Kingery–Bulmash-style analysis approach and calculate the characteristic fitting parameters for time of arrival of the microshock. Blast waves from these laser energies cover scaled distances of ~  2–50 m/\(\hbox {kg}^{\mathrm {1/3}}\), roughly equivalent to the detonation of a few grams of TNT probed from several meters away. We compare the experimental results to BlastX simulations and tabulated data from a variety of sources. Under this experimental configuration, a 302-mJ laser pulse is equivalent to a TNT charge in the mass range 1–18 \(\upmu \)g and the 628-mJ pulse is within the range 10–45 \(\upmu \)g. This corresponds to a laser energy to shock coupling ratio when compared to 100% TNT equivalence of 1–24% and 7–29%, respectively. This work informs microblast scaling expectations for experiments using laser-induced shock waves as a microscale energetic characterization technique and provides connections between laboratory and free-field detonation testing.