Ultrafast dynamics and sub-wavelength periodic structure formation following irradiation of GaAs with femtosecond laser pulses

TL;DR

This paper presents a theoretical study of ultrafast carrier dynamics in GaAs under femtosecond laser pulses, linking transient carrier densities to damage thresholds and surface structure formation, with experimental validation.

Contribution

It introduces a detailed multiscale model connecting carrier excitation, damage thresholds, and sub-wavelength structure formation in GaAs during femtosecond laser irradiation.

Findings

Carrier density correlates with damage threshold depending on pulse duration.

Fluence levels induce metallic behavior in GaAs.

Surface plasmon waves contribute to periodic structure formation.

Abstract

A theoretical investigation of the ultrafast processes and dynamics of the excited carriers upon irradiation of GaAs with femtosecond (fs) pulsed lasers is performed in conditions that induce material damage and eventually surface modification of the heated solid. A parametric study is followed to correlate the produced transient carrier density with the damage threshold for various pulse duration values {\tau}p (it increases as ~ at relatively small values of {\tau}p while it drops for pulse durations of the order of some picoseconds) based on the investigation of the fundamental multiscale physical processes following fs-laser irradiation. Moreover, fluence values for which the originally semiconducting material demonstrates a metallic behaviour are estimated. It is shown that a sufficient number of carriers in the conduction band are produced to excite Surface Plasmon (SP) waves that upon coupling with the incident beam and a fluid-based surface modification mechanism lead to the formation of sub-wavelength periodic structures orientated perpendicularly to the laser beam polarization. Experimental results for the damage threshold and the frequencies of induced periodic structures show a good agreement with the theoretical predictions.