Damage threshold evaluation of thin metallic films exposed to femtosecond laser pulses: the role of material thickness

TL;DR

This paper presents a theoretical analysis of how material thickness and photon energy influence the damage threshold of thin metallic films under femtosecond laser pulses, aiding in optimized laser fabrication.

Contribution

It introduces a multiscale physical model that links optical, thermal, and material responses to predict damage thresholds for various metals based on thickness and laser parameters.

Findings

Damage threshold varies with material thickness and photon energy.

The model aligns well with experimental data.

Insights can improve laser processing precision.

Abstract

The employment of femtosecond pulsed lasers has received significant attention due to its capability to facilitate fabrication of precise patterns at the micro- and nano- lengths scales. A key issue for efficient material processing is the accurate determination of the damage threshold that is associated with the laser peak fluence at which minimal damage occurs on the surface of the irradiated solid. Despite a wealth of previous reports that focused on the evaluation of the laser conditions that lead to the onset of damage, the investigation of both the optical and thermal response of thin films of sizes comparable to the optical penetration depth is still an unexplored area. In this report, a detailed theoretical analysis of the impact of various parameters such as the photon energies and material thickness on the damage threshold for various metals (Au, Ag, Cu, Al, Ni, Ti, Cr, Stainless Steel) is investigated. A multiscale physical model is used that correlates the energy absorption, electron excitation, relaxation processes and minimal surface modification which leads to the onset of material damage. The satisfactory agreement of the theoretical model with some experimental results indicates that the damage threshold evaluation method could represent a systematic approach towards designing efficient laser-based fabrication systems and optimizing the processing outcome for various applications.