Volume nanograting formation in laser-silica interaction as a result of the 1D plasma-resonance ionization instability

TL;DR

This paper investigates the initial ionization-induced instability inside fused silica under femtosecond laser pulses, revealing a hybrid 1D structure with a period matching experimental nanograting observations.

Contribution

It introduces the calculation of the spatial spectra of the instability considering electron-hole diffusion, explaining nanograting formation as a plasma-resonance ionization instability.

Findings

The instability results in a hybrid diffusion-wave structure.

The spatial period is approximately the laser half-wavelength.

The period matches experimental nanograting measurements.

Abstract

The initial stage of the small-scale ionization-induced instability developing inside the fused silica volume exposed to the femtosecond laser pulse is studied as a possible initial cause of the self-organized nanograting formation. We have calculated the spatial spectra of the instability with the electron-hole diffusion taken into account for the first time and have found that it results in the formation of some hybrid (diffusion-wave) 1D structure with the spatial period determined as geometrical mean of the laser wavelength and characteristic diffusion length of the process considered. Near the threshold of the instability this period occurs to be approximately equal to the laser half-wavelength in the silica, close to the one experimentally observed.