Self-Gompression and Self-Focusing Instability of Femtosecond Multiterawatt Laser Pulses in Underdense Plasmas

Self-compression and self-focusing instabilities of femtosecond, multiterawatt laser pulses propagating at subrelativistic intensities in strongly undercritical plasmas are studied. Our numerical simulations show that the spatiotemporal self-compression works effectively in underdense (1% of the critical density) plasmas and relativistically intense, few-cycle laser pulses can be produced in this way over propagation distances less than 2 mm. We found that pulses with Gaussian radial and time profiles are very robust maintaining their initial shape and proportions during this process, while, in general, the interplay between the self-compression and the self-focusing has proved to be very sensitive to the shape of laser pulses.