Femtosecond two-photon-excited backward lasing of atomic hydrogen in flame

TL;DR

This paper demonstrates femtosecond two-photon excitation inducing backward lasing of atomic hydrogen in flames, enabling spatially resolved hydrogen concentration measurements with high temporal resolution.

Contribution

It is the first to observe and characterize backward-propagating hydrogen lasing in flames using femtosecond two-photon excitation, providing a new diagnostic method.

Findings

Backward lasing at 656 nm observed in flames

Lasing pulse duration is on the picosecond scale

Method enables spatially resolved hydrogen measurements

Abstract

We report on an observation of bi-directional 656 nm lasing action of atomic hydrogen in premixed CH4/air flame induced by resonant femtosecond 205 nm two-photon excitation. In particular, the backward-propagating lasing pulse is systematically characterized in the spectral, spatial and temporal domains for the sake of single-ended diagnostic. Its picosecond-scale duration enables spatially resolved concentration measurements of hydrogen atoms in millimeter range, which is successfully demonstrated using two narrow welding flames.