Initial power compression efficiency of relativistic laser self-channeling in an experimental xenon gas target

The initial power compression efficiency of relativistic laser self-channeling in experimental xenon gas has been investigated numerically with a modified model. The axial and transverse density profile of electron plasma generated by the front temporal region of the laser pulse through ionization varies from the gas density profile due to the laser intensity-dependent ionization properties of the gas medium, and is thus determined by ionization condition, laser vacuum focusing condition, xenon gas density, and the laser power. These conditions also decide the laser self-focusing starting position. This axial self-focusing position might be either before or after the vacuum focal position. The results show that, in contrast to the previous model, the axial gas density gradient does not always affect the initial power compression efficiency of self-channeling positively compared to the step-function gas density case; even with some cases, power cannot be compressed to form a channel. The results outline the more realistic laser-xenon target conditions that must be met to increase the power compression efficiency of self-channeling. In addition to a higher incident power and smaller initial laser spot size at the beam collapse position being favorable for efficient initial power compression, for lasers with larger vacuum focal spot sizes, a steeper axial gas density gradient is also needed to form a channel.