Experimental study of relativistic self-focusing and self-channeling of an intense laser pulse in an underdense plasma

摘要

This paper reports on experimental investigations on relativistic self-focusing and self-channeling of a terawatt laser pulse (0.7 TW/spl les/P/spl les/15 TW) in an underdense plasma. We present results obtained with picosecond (/spl tau/=1 ps) and subpicosecond (/spl tau/=0.4 ps) pulses. In the "long pulse" regime, modifications in the laser propagation are observed for P>P/sub c/, the critical power for self-focusing. By contrast, self-guiding of subpicosecond pulses is observed for P/spl ap/P/sub c/. Using a paraxial envelope model describing the laser propagation and taking into account the plasma response to the ponderomotive force, it is shown that a maximum laser intensity of 5-15 times that reached in vacuum may be achieved when P is in the (1.25-4)/spl times/P/sub c/ range. It is also demonstrated that ion motion may significantly reduce the effective P/sub c/.