Laser Induced Tunnel Ionization and Electron Density Evolution in Air

Abstract

An indigenously built Ti:sapphire laser system delivering 50 mJ, 100 fs pulses at a repetition rate of 10 Hz, is employed to tunnel ionize air at 1 atm pressure and form a plasma channel. The laser is line focused using a cylindrical lens to a spot size of 20μm×1mm. A folded wave interferometry is used to deduce the radial electron density profile by measuring the phase shift and employing Abel inversion. The maximum value of chord-integrated electron density and radial electron density are estimated to be approximately equal to 3.0×10¹⁶ cm⁻² and 4.0×10¹⁸ cm⁻³ respectively with density scale length of 20 μm. These results have been theoretically interpreted by developing a unified formalism of tunnel ionization. The experimental results are in reasonable agreement with the theory.