# Orientation of ripples induced by ultrafast laser pulses on copper in different liquids

## TL;DR

This study investigates how ultrafast laser pulses create and control ripple patterns on copper surfaces in different liquids, revealing orientation changes with laser intensity and multi-directional structures.

## Contribution

It demonstrates the formation and orientation control of laser-induced ripples on copper in various liquids using femtosecond pulses, including multi-directional structures.

## Key findings

- Ripples can be oriented perpendicular or parallel to laser polarization.
- Ripple orientation changes with incident light intensity.
- Multi-directional ripple formation occurs in liquids.

## Abstract

Formation of laser-induced periodic surface structures (LIPSS or ripples) was studied on a metallic surface of polished copper by using irradiation with multiple femtosecond laser pulses in different environmental conditions (air, water, ethanol and methanol). Uniform LIPSS have been achieved by controlling the peak fluence and the overlapping rate. Ripples in both orientations, perpendicular and parallel to laser polarization, were observed in all liquids simultaneously. The orientation of these ripples in the center of the ablated line was changing with the incident light intensity. For low intensities the orientation of the ripples is perpendicular to the laser polarization, whereas for high intensities it turns parallel to it without considerable changes in the period. Multi-directional LIPSS formation was also observed for moderate peak fluence in liquid environments.