Laser-driven detonation wave in a dielectric film prior to ablation

Illumination of hafnium dioxide (HfO2) thin films with a nanosecond pulsed laser reaching peak intensities of 180  GW  /  cm2 has been shown to trigger a laterally expanding plasma wave prior to ablation that reaches speeds of up to 100  km  /  s. The phenomenon has recently been described as a defect-initiated laser-driven detonation (LDD) wave propagating in the electron–hole subspace, but the electron/hole effective masses that would be required for quantitative agreement were found to be at least 100 times heavier than band structure calculations predicted for HfO2. The results are re-examined in the context of a more general description of LDD that accounts for a change in the electron effective mass between the pre- and post-detonation states. Reasonable agreement between theory and experiment is found under the assumption that the electron’s effective mass decreases by a factor of 20 and approaches the free electron mass in the final state.