Effect of self-injection on ultra-intense laser wake field acceleration

Abstract. The effect of self-injection originated from the relativistic acceleration of plasma electrons by a laser pulse moving with group velocity less than the light speed is found through particle-in-cell simulation to be efficient for the laser wake field acceleration at Iλ2>5x1019 W µm2/cm2. At matching condition a02/2=ω/ωpl, the self-injection, along with the wave-breaking, dominates electron acceleration up to GeV energy by a 100 TW, 20 fs laser pulse. In contrast to the injection due to wave-breaking processes, the self-injection allows to avoid the maxwellization of accelerated particles and to extract a beam-quality bunch of energetic electrons. The laser wake-field acceleration (LWFA) of electrons in underdense plasmas [1] has been a subject of intense study for many years. This process is expected to be a good basis for efficient and compact electron accelerators [2-5]. However, in the case of laser pulses with relativistic intensity, Iλ2>1019 Wµm2/cm2, the electron acceleration by the wake-field is not well understood in spite of several experimental [2-4] and numerical [6,7] works. Recently, necessity of short-pulse (~10 fs) electron beams with total charge large enough for the probe-analysis [8,9] raises interest to the laser wake-field acceleration as a promising source for such beams. Due to the small length of acceleration [5], the LWF