Formation of periodic surface structures on dielectrics after irradiation with laser beams of spatially variant polarisation: a comparative study

TL;DR

This study compares how different laser beam polarizations affect the formation of periodic surface structures on dielectrics, revealing the influence of laser parameters and polarization on surface patterning mechanisms.

Contribution

It provides a comparative analysis of surface structure formation under radially and azimuthally polarized femtosecond laser irradiation, including a theoretical model for periodicity prediction.

Findings

Azimuthally polarized beams produce smaller periodic structures.

Increased laser pulses enhance structure prominence.

Structure orientation aligns with laser polarization.

Abstract

A comparative study is performed to explore the periodic structure formation upon intense femtosecond pulsed irradiation of dielectrics with radially and azimuthally polarised beams. Laser conditions have been selected appropriately to produce excited carriers with densities below the optical breakdown threshold in order to highlight the role of phase transitions in surface modification mechanisms. The frequency of the laser induced structures is calculated based on a theoretical model that comprises estimation of electron density excitation, heat transfer, relaxation processes, and hydrodynamics-related mass transport. The influence of the laser wavelength in the periodicity of the structures is also unveiled. The decreased energy absorption for azimuthally polarised beams yields periodic structures with smaller frequencies which are more pronounced as the number of laser pulses applied to the irradiation spot increases. Similar results are obtained for laser pulses of larger photon energy and higher fluences. All induced periodic structures are oriented parallel to the laser beam polarisation.