Laser-triggered terahertz emission from near-critical-density targets.

Femtosecond laser pulse propagation in a relativistic self-trapping (RST) regime in a near-critical density plasma makes it possible to maximize the total charge of the accelerating electrons and laser-to-electrons conversion rate, that can be used to provide a large amount of the terahertz range coherent transition radiation. The three-dimensional particle-in-cell simulations demonstrate how such transition radiation generates when electrons escape into vacuum either from the low-density target itself, or after passing through a thin foil located at the target end. The advantage of the RST regime for the generation of terahertz pulses is clearly demonstrated as compared to laser irradiation of such a standard target as a foil with preplasma on its front side.

Compression of high-power laser pulse leads to increase of electron acceleration efficiency.

Propagation of ultrarelativistically intense laser pulses in a self-trapping mode in a near critical density plasma makes it possible to produce electron bunches of extreme parameters appropriate for different state of the art applications. Based on three-dimensional particle-in-cell (PIC) simulations, it has been demonstrated how the best efficiency of electron acceleration in terms of the total charge of high-energy electrons and laser-to-electron conversion rate can be achieved. For a given laser pulse energy the universal way is a proper matching of laser hot spot size and electron plasma density to the laser pulse duration.