The clamped intensity of femtosecond laser pulses varying with gas pressure in the presence of external focusing

TL;DR

This paper theoretically studies how the maximum laser intensity inside a filament varies with gas pressure when external focusing is used, revealing a pressure-dependent behavior unlike self-focusing.

Contribution

It introduces a model showing that external focusing causes the clamped intensity to decrease with increasing gas pressure, unlike self-focusing conditions.

Findings

Clamped intensity decreases with gas pressure under external focusing.

The model explains pressure-dependent changes in femtosecond laser emissions.

Results align with experimental observations of nitrogen fluorescence.

Abstract

We perform a theoretical investigation of the clamped laser intensity inside the filament plasma as a function of gas pressure with external focusing. Unlike the clamped intensity under the selffocusing condition, which is independent on the gas pressure, the clamped intensity with external focusing decreases with the gas pressure. Our findings can explain the changes of the signals of femtosecond-laser-induced 391-nm forward emission and fluorescence with the nitrogen gas pressure.