Observation of strong correlation between quasimonoenergetic electron beam generation by laser wakefield and laser guiding inside a preplasma cavity

We use a one-shot measurement technique to study effects of laser prepulses on the electron laser wakefield acceleration driven by relativistically intense laser pulses (λ=7900.3em0exnm, 110.3em0exTW, 370.3em0exfs) in dense helium gas jets. A quasimonoenergetic electron bunch with an energy peak ~11.50.3em0exMeV [ΔE∕E~10% (FWHM)] and with a narrow-cone angle (0.04π0.3em0exmm0.2em0exmrad) of ejection is detected at a plasma density of 8×10¹⁹0.3em0excm^-3. A strong correlation between the generation of monoenergetic electrons and optical guiding of the pulse in a thin channel produced by picosecond laser prepulses is observed. This generation mechanism is well corroborated by two-dimensional particle-in-cell simulations.