QUANTITATIVE STUDY OF THE IONIZATION-INDUCED REFRACTION OF PICOSECONDLASER-PULSES IN GAS-JET TARGETS

A quantitative study of refractive whole beam defocusing and small sca le breakup induced by optical ionization of subpicosecond and picoseco nd, 0.25 and 1 mu m, laser pulses in gas-jet targets at densities abov e 1 x 10(19) cm(-3) has been carried out. A significant reduction of t he incident laser intensity was observed due to refraction from ioniza tion-induced density gradients. The level of refraction measured with optical probing correlated well with the fraction of energy transmitte d through the plasma. The numerical and analytical models were found t o agree well with experimental observations.