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.