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. The recommendation to achieve the highest yield of high-energy electrons is to compress the laser pulse as much as possible. As an example, compression of a pulse of a few tens of femtoseconds to the <^>'10 fs pulse leads to generation of the high-energy electron bunch with the highest total charge to exhibit conversion efficiency exceeding 50% for the Joule-level laser pulse energies.