Optically shaped mass-limited liquid sheet target for high repetition rate laser-driven acceleration

A fully optical approach for the generation of a mass-limited thin liquid sheet target and its implementation in repetitive laser-plasma electron acceleration experiments was demonstrated. The target with an estimated thickness of a few micrometers was obtained by optical shaping of a pure ethanol droplet gently irradiated by a low-energy nanosecond laser pulse, experiencing lensing inside the droplet and causing energy deposition by the breakdown. The propulsion of the droplet results on a timescale of a few hundred nanoseconds in a thin sail formation oriented toward the incident laser radiation, having a high spatial stability. Even higher stability was obtained using a femtosecond shaping pulse, ensuring efficient ionization. A multi-MeV energy electron beam was generated by the double-pulse irradiation of the sail target, where the first intense nanosecond pulse bores the preformed thin liquid sheet and forms an under-critical plasma slab, and the second, relativistically intense femtosecond pulse accelerates particles when propagating through the plasma. The deduced optimal temporal delay between the latter two pulses supports estimates on the small sail thickness.