Ionization clamping in ultrafast optical breakdown of transparent solids

TL;DR

This paper introduces a multi-physics model for ultrafast laser propagation in transparent solids, revealing ionization is capped at a fraction of the valence band electron density, and revises pressure estimates for laser-induced breakdown.

Contribution

It presents a novel multi-physics model that accurately describes ionization dynamics and pressure limits during ultrafast laser breakdown in transparent dielectrics.

Findings

Ionization is universally clamped at about 10% of the valence band electron density.

Previous pressure estimates (~10 TPa) are overestimated by two orders of magnitude.

The model provides new insights into laser-induced breakdown mechanisms.

Abstract

We formulate a multi-physics model to describe the nonlinear propagation of a femtosecond, near-infrared, tightly focused laser pulse in a transparent dielectric. The application of our model to the case of bulk sapphire shows that even under extreme excitation conditions, ionization is universally clamped at about one tenth of the electron density in the upper valence band. The earlier estimate of ~10 TPa pressure that could be attainable through the internal excitation of transparent dielectrics by tightly focused ultrafast laser beams is shown to be off by two orders of magnitude.