Interferometry in Femtosecond Laser Plasma Diagnostics

Electron density dynamics in air, nitrogen and argon femtosecond filament plasma channel is studied under different pressure up to hundreds of picoseconds after ionization by transverse interferometry method. It is revealed that initial electron density in nitrogen plasma rises significantly under the pressure over 4 atmospheres. Optical refractive index anisotropy, which precedes and accompanies ionization, related with intense pulse propagation is revealed.