2-DIMENSIONAL EFFECTS IN A TUNNEL IONIZED PLASMA

An intense short pulse laser of finite spot size propagating through a gas produces plasma via tunnel ionization on a femtosecond time scale . The radial profile of plasma density is strongly peaked on the axis and has a defocusing property. As electron density grows with time, th e trailing part of the laser pulse suffers stronger divergence than th e leading front, causing severe temporal distortion of the pulse. A se lf-consistent paraxial ray theory of electron density evolution and de focusing of the laser reveals that a square (in time) laser pulse, aft er propagating one Rayleigh length, has an order of magnitude differen ce in the axial intensity at the front and the tail of the pulse. (C) 1997 American Institute of Physics.