Suppression of ablation in femtosecond double pulse experiments

TL;DR

This paper investigates why crater depth decreases in femtosecond double pulse experiments at long delays, revealing that the second pulse suppresses ablation by interacting with expanding material and forming a shock wave.

Contribution

It provides a detailed hydrodynamic model explaining the suppression of ablation in femtosecond double pulse laser experiments at delays exceeding electron-ion relaxation time.

Findings

Ablation is suppressed when pulse delay exceeds electron-ion relaxation time.

Second pulse interacts with expanding material, forming a shock wave.

Pressure and density profiles confirm suppression mechanism.

Abstract

We report the physical reasons of a curious decrease in the crater depth observed for long delays in experiments with femtosecond double pulses. Detailed hydrodynamic modeling demonstrates that the ablation mechanism is dumped when the delay between the pulses exceeds the electron-ion relaxation time. In this case, the interaction of the second laser pulse with the expanding target material leads to the formation of the second shock wave suppressing the rarefaction wave created by the first pulse. The evidence of this effect follows from the pressure and density profiles obtained at different delays after the first laser pulse.