Production and application of short electron bunches from the interaction of high-intensity lasers with tenuous plasma.

摘要

A series of experiments have been performed using sub-picosecond terawatt CPA-based laser systems to study the production and applications of short electron bunches from under-dense plasma. Two studies were conducted using laser pulses that were long (400 fs) compared to the plasma period, tau laser " 2pi/oplasma. In one experiment on pulse radiolysis, a laser-produced nC-ps electron bunch is reported for the first time to have triggered chemical reactions in pure water, which were monitored and recorded. In another case, two orthogonally-crossed TW laser beams, spatially and temporally overlapped, were studied theoretically and experimentally. Their confluence was found to form a novel optical trap. It was inferred from their interference fringes that the trap depth was deep enough to ponderomotively confine plasma electrons to within less than a laser wavelength, with a density modulation 10 times the ambient plasma density, and an average DC electric field approaching TV/m (1012 V/m). This overlap also enhanced the production and quality of the electron beam as compared to a single beam. Further investigations were carried out in the short pulse, or resonant regime, tau laser = 30 fs ∼ 2pi/oplasma, in order to examine the feasibility of a novel laser accelerator scheme that was proposed to mitigate the shortcomings in the quality of the current laser-accelerator-produced electron beams. In this concept called LILAC (Laser Injected Laser ACcelerator), two short laser pulses, comparable in duration to a single plasma period, intersect synchronously in under-dense plasma. One pulse assumes the role of resonantly exciting a wake, and the other one locally alters the trajectories of the background plasma electrons, causing them to be trapped and accelerated in the wake. In so doing, this produces shorter bunches, narrower energy distribution and does not rely on the plasma instability of current laser wakefield accelerators. An experiment that was performed showed that in the parameter regime of this proposed laser accelerator the filamentation instability and dark current from self-trapping are not undesirably too high.