Quantitative Study of the Ionization-Induced Refraction of Picosecond Laser Pulses in Gas-Jet Targets

A quantitative study of refractive whole beam defocusing and small scale breakup induced by optical ionization of subpicosecond and picosecond, 0.25 and 1 μm, laser pulses in gas-jet targets at densities above $1\times {10}^{19}{\mathrm{cm}}^{-3\mathrm{}}$ has been carried out. A significant reduction of the incident laser intensity was observed due to refraction from ionization-induced density gradients. The level of refraction measured with optical probing correlated well with the fraction of energy transmitted through the plasma. The numerical and analytical models were found to agree well with experimental observations.