Laser-driven detonation wave in hafnium oxide film: Defect controlled laser damage and ablation

An ion-beam sputtered film of hafnium oxide was irradiated with an intense nanosecond laser pulse above the ablation threshold. The transmitted laser power was measured as a function of time, with a resolution of a few hundred picoseconds. The spatial origin of the defect-triggered ablation was monitored for each event. A phenomenological model of a rapidly expanding, absorbing disk can explain the observed time dependent transmission and structure sizes of the affected material. The required expansion speeds, ranging from 1 to 100 km/s, and their observed dependence on the local laser intensity, are compatible with a laser-driven detonation wave as described by the Chapman–Jouget (CJ) theory. Because the energy deposited by the laser pulse is too low to explain detonation in a material with the density of hafnium oxide, we hypothesize that the detonation wave propagates in the electron–hole subspace. We modified the CJ theory to describe laser-driven detonation in an electron–hole plasma and to account for plasma expansion sideways to the laser beam.