Energy deposition from focused terawatt laser pulses in air undergoing multifilamentation

TL;DR

This study investigates how focused terawatt laser pulses cause energy deposition in air through multifilamentation, leading to heat, shock waves, and the formation of a low-density channel over microsecond timescales.

Contribution

It provides the first detailed measurement of energy transfer and hydrodynamic effects from multifilamentation of high-power laser pulses in air.

Findings

Over 60% of pulse energy is transferred to heat in air.

Formation of a single low-density channel from merging filaments.

Maximum lineic energy deposition exceeds 1 J/m.

Abstract

Laser filamentation is responsible for the deposition of a significant part of the laser pulse energy in the propagation medium. We found that using terawatt laser pulses and relatively tight focusing conditions in air, resulting in a bundle of co-propagating multifilaments, more than 60 % of the pulses energy is transferred to the medium, eventually degrading into heat. This results in a strong hydrodynamic reaction of air with the generation of shock waves and associated underdense channels for each short-scale filament. In the focal zone, where filaments are close to each other, these discrete channels eventually merge to form a single cylindrical low-density tube over a $\sim 1 \mu\mathrm{s}$ timescale. We measured the maximum lineic deposited energy to be more than 1 J/m.