Laser steepening controls polarization-dependent electron self-injection in laser plasma accelerators

An intense laser pulse propagating inside plasma can form a shock-like steepened front. After the onset of pulse steepening, bubble formed by the laser pulse undergoes expansion and transverse undulation [1]. Bubble undulation is periodic in time and is controlled by laser polarization and Carrier-Envelope-Phase (CEP) [2].  Expansion and undulation can modify electron trapping from background plasma: expansion can help trap electrons, but undulation can both enhance or suppress trapping. Their interplay gives rise to a complex trapping process periodic in space and time controlled by laser pulse CEP and polarization. By changing laser polarization from linear to circular, structure of the injected electron beam can be changed from a fs-scale modulated beam or a flat current profile. Furthermore, the high charge  few nC injected electrons leads to efficient energy conversion from the laser pulse to injected electrons. This injection mechanism is amenable to several existing TW-scale few-cycle to multi-cycle laser pulses.

[1] Ma, Yong, et al. Scientific Reports. 5,30491(2016)

[2] E.N.Nerush and I.Yu.Kostyukov, Phys.Rev.Lett. 103,035001(2009)