Universal threshold for femtosecond laser ablation with oblique illumination

TL;DR

This study demonstrates that the ablation threshold fluence for femtosecond lasers is universally independent of incidence angle and polarization across different materials, enabling improved laser beam profiling.

Contribution

It introduces a universal threshold fluence concept for femtosecond laser ablation that is unaffected by angle and polarization, despite nonlinear ionization dynamics.

Findings

Threshold fluence is independent of angle and polarization.

Universal applicability across metal, dielectric, and semiconductor.

Potential for improved laser beam profiling techniques.

Abstract

We quantify the dependence of the single-shot ablation threshold on the angle of incidence and polarization of a femtosecond laser beam, for three dissimilar solid-state materials: a metal, a dielectric and a semiconductor. Using the constant, linear value of the index of refraction, we calculate the laser fluence transmitted through the air-material interface at the point of ablation threshold. We show that, in spite of the highly nonlinear ionization dynamics involved in the ablation process, the so defined transmitted threshold fluence is universally independent of the angle of incidence and polarization of the laser beam for all three material types. We suggest that angular dependence of ablation threshold can be utilized for profiling fluence distributions in ultra-intense femtosecond laser beams.