Unraveling the formation dynamics of metallic femtosecond laser induced periodic surface structures

TL;DR

This paper develops a comprehensive theoretical model combining thermal and fluid dynamics to understand the formation of laser-induced periodic surface structures on metals, validated by experiments on stainless steel.

Contribution

It introduces a novel simulation framework that accurately predicts LIPSS morphology and depth, advancing the understanding of femtosecond laser surface processing dynamics.

Findings

Theoretical results match experimental AFM measurements.

LIPSS topology and depth depend on the number of laser pulses.

The model provides insights into controlling surface structures for applications.

Abstract

Femtosecond laser surface processing (FLSP) is an emerging fabrication technique to efficiently control the surface morphology of many types of materials including metals. However, the theoretical understanding of the FLSP formation dynamics is not a trivial task, since it involves the interaction of various physical processes (electromagnetic, thermal, fluid dynamics) and remains relatively unexplored. In this work, we tackle this problem and present rigorous theoretical results relevant to low-fluence FLSP that accurately match the outcomes of an experimental campaign focused on the formation dynamics of laser induced periodic surface structures (LIPSS) on stainless steel. More specifically, the topology and maximum depth of LIPSS trenches are theoretically and experimentally investigated as a function of the number of laser pulses. Moreover, precise LIPSS morphology measurements are performed using atomic force microscopy (AFM). The proposed comprehensive simulation study is based on two-temperature model (TTM) non-equilibrium thermal simulations coupled with fluid dynamic computations to capture the melting metal phase occurring during FLSP. Our rigorous simulation results are found to be in excellent agreement with the AFM measurements. The presented theoretical framework to model FLSP under low-fluence femtosecond laser pulses will be beneficial to various emerging applications of LIPSS on metallic surfaces, such as cooling high-powered laser diodes and controlling the thermal emission or absorption of metals.