SELF-MODULATION OF LASER-PULSES IN PLASMA AND LASER ACCELERATION OF ELECTRONS

In an underdense plasma, the role of relativistic and ponderomotive se lf-focusing in the self-modulation of shea and powerful laser pulses i s studied. It is shown that, with the help of a second weak-intensity laser pulse with a carrier frequency shifted by the value of the plasm a frequency with respect to that of the main pulse, in plasma channels , it is possible to obtain a pulse self-modulation resulting in the ex citation of large-amplitude plasma waves over a distance of many Rayle igh lengths. The features of such an excitation are studied and the ad vantages of using a self-modulated pulse for the generation of a plasm a wave are discussed and compared with the other schemes discussed in relation to the laser accelerator.