Thermal response and optical absorptance of metals under femtosecond laser irradiation

Anatoliy Y Vorobyev,Chunlei Guo

doi:10.4236/ns.2011.36068

Abstract

A detailed study on correlation between residual thermal response of a sample and its optical absorptance change due to laser-induced sur-face structural modifications in multi-shot fem-tosecond laser irradiation is performed. Ex-periments reveal an overall enhancement for residual thermal coupling and absorptance in air. Surprisingly, residual thermal coupling in air shows a non-monotonic dependence on pulse number and reaches a minimum value after a certain number of pulses, while these behaviors are not seen in absorptance. In vacuum, how-ever, both suppression and enhancement are seen in residual energy coupling although ab-sorptance is always enhanced. From these ob-servations, it appears that air plasma plays a dominant role in thermal coupling at a relatively low number of applied pulses, while the forma-tion of craters plays a dominant role at a high number of pulses.

Highlights

IntroductionMany applications of femtosecond lasers, such as high-precision materials machining [1,2], nanotechnology [3,4,5,6,7], modification of optical properties of materials [8,9,10,11,12], thin film deposition [13], modification of wetting properties of solids [14,15,16,17], producing diamond-like materials [18], laser plasma thrusters [19], and biomedicine [17,20], are based on laser ablation of solids
Recent studies have shown that the residual thermal energy in an irradiated metal sample abruptly increases following both single-pulse and pulse-train femtosecond laser ablation in a gas medium when the laser fluence is above a certain threshold [28,29]
We perform a shot-to-shot detailed study on how residual thermal coupling depends on the absorptance change due to laser-induced surface structural modifications

Summary

Introduction

Many applications of femtosecond lasers, such as high-precision materials machining [1,2], nanotechnology [3,4,5,6,7], modification of optical properties of materials [8,9,10,11,12], thin film deposition [13], modification of wetting properties of solids [14,15,16,17], producing diamond-like materials [18], laser plasma thrusters [19], and biomedicine [17,20], are based on laser ablation of solids. Residual thermal coupling in air shows a non-monotonic dependence on pulse number and reaches a minimum value after a certain number of pulses, while these behaviors are not seen in absorptance. In vacuum, both suppression and enhancement are seen in residual energy coupling absorptance is always enhanced. Both suppression and enhancement are seen in residual energy coupling absorptance is always enhanced To explain these observations, we suggest that air plasma plays a dominant role in thermal coupling at a relatively low number of applied pulses while the formation of craters plays a dominant role at a high number of pulses

Methods

Results

Conclusion