The Role of Plasma Shielding in Double-Pulse Femtosecond Laser-Induced Breakdown Spectroscopy

TL;DR

This paper investigates how plasma shielding affects the enhancement of optical emission in double-pulse femtosecond laser-induced breakdown spectroscopy, combining experimental measurements and particle-in-cell simulations.

Contribution

It provides a detailed mechanism explaining the enhancement effect, showing plasma shielding as the key factor, which was not previously well understood.

Findings

Plasma produced by the first pulse shields the surface from the second pulse for delays up to 100 ps.

Enhanced emission is due to excitation of particles in the plasma, not additional ablation.

Experimental and theoretical results agree on the plasma shielding mechanism.

Abstract

It is well known that optical emission produced by femtosecond laser-induced breakdown on a surface may be enhanced by using a pair of laser pulses separated by a suitable delay. Here we elucidate the mechanism for this effect both experimentally and theoretically. Using a bilayer sample consisting of a thin film of Ag deposited on an Al substrate as the ablation target and measuring the breakdown spectrum as a function of fluence and pulse delay, it is shown experimentally that the enhanced signal is not caused by additional ablation initiated by the second pulse. Rather, particle-in-cell calculations show that the plasma produced by the first pulse shields the surface from the second pulse for delays up to 100 ps. These results indicate that the enhancement is the result of excitement of particles entrained in the plasma produced by the first pulse.