# Correlated emission of X-ray and sound from water film irradiated by femtosecond laser pulses

## TL;DR

This study investigates the simultaneous generation of X-ray and sound from a water film irradiated by femtosecond laser pulses, revealing correlated emission profiles and enhancement effects under double-pulse conditions.

## Contribution

It demonstrates the correlated emission of X-ray and sound from water films and explores how double-pulse laser irradiation enhances these emissions through ablation dynamics.

## Key findings

- X-ray and sound emissions have similar peak positions with different emission widths.
- Double-pulse irradiation enhances both X-ray and sound signals.
- Acoustic signals show weak dependence on pre-pulse position due to filament formation.

## Abstract

Simultaneous measurements of hard X-ray by a Geiger counter and audible sound (10 Hz-20kHz) by a microphone from a thin water film in air were carried out under intense single and double pulse irradiations of femtosecond laser (35 fs, 800 nm, 1 kHz). Emission profiles of X-ray and sound under the single pulse irradiation by changing the water film position along the laser incident direction (Z-axis) show the same peak positions with a broader emission in sound (403{\mu}m at FWHM) than in X-ray (37{\mu}m). Under the double pulse irradiation condition with the time delay at 0 ps and 4.6 ns, it was clearly observed that the acoustic signal intensity is enhanced in associated with X-ray intensity enhancements. The enhancements can be assigned to laser ablation dynamics such as pre-plasma formation and transient surface roughness formation induced by the pre-pulse irradiation. For the acoustic signal under the double-pulse irradiation with the time delay, there was a weak dependence observed on the pre-pulse irradiation position at the laser focus. It is consistent with a long breakdown filament formation which makes the microphone-detection less position-sensitive.