Direct measurement of electron numbers created at infrared laser-induced ionization of various gases

TL;DR

This study directly measures electron numbers generated by femtosecond laser ionization of various gases using microwave scattering, revealing decay dynamics influenced by ionization and recombination processes.

Contribution

It provides the first temporally resolved measurements of electron numbers at laser-induced ionization across multiple gases using microwave scattering.

Findings

Electron numbers ranged from 3×10^8 to 3×10^12.

Decay times varied from 1 to 40 ns depending on the gas.

Ionization and recombination processes govern plasma decay.

Abstract

In this work, we present temporally resolved measurements of electron numbers created at photoionization of various gases by femtosecond laser pulse at 800 nm wavelength. The experiments were conducted in $O_2$, $Xe$, $Ar$, $N_2$, $Kr$ and $CO$ at room temperature and atmospheric pressure. Elastic microwave scattering was used to directly measure the electron numbers. Numbers of electrons in the range $3*10^8$ to $3*10^{12}$ electrons were produced by the laser pulse energies 100-700 uJ. After the laser pulse, plasma decayed on the time scale varied from 1 to 40 ns depending on the gas type and governed by two competing processes, namely, the creation of new electrons from ionization of the metastable atoms and loss of the electrons due to dissociative recombination and attachment to oxygen.