Wakefield generation by elliptically polarized femtosecond laser pulse in ionizing gases

Wakefield generation by a femtosecond laser pulse is described in the frame of the slowly varying amplitudes approximation, The amplitude of the wakef ield A(p) is studied as a function of Laser pulse and background gas parame ters, and is compared with well-known results for preformed, completely ion ized plasma A(p,i). It is found that the ionization processes can increase A(p) as compared to A(p,i) at comparatively high laser peak intensities. It is shown that the increase of the wakefield amplitude due to gas ionizatio n is more pronounced for circularly polarized laser pulses than for Linearl y polarized laser pulses, The strongest enhancement of A(p) in comparison w ith A(p,i) takes place for longer laser pulses with a duration in excess of the plasma wave period when the resonant conditions fur ponderomotive exci tation of the wakefield are not matched, Thus, ionization processes can exp and the region of parameters for efficient generation of the laser wakefiel ds.