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

In this work, we present temporally resolved measurements of electron numbers created at photoionization of various gases by a femtosecond-laser pulse at 800 nm wavelength. The experiments were conducted in O₂, Xe, Ar, N₂, 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 × 10⁸-3 × 10¹² were produced by the laser pulse energies 100-700 μJ. After the laser pulse, plasma decayed on the time scale 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.