Characteristics of the preplasma formation using an uncompressed picosecond-long laser pulse with a large spot size on Al and mylar targets

A preplasma plays a very important role in laser-driven proton acceleration, where it can increase the proton energy significantly. In this research, we generated a nearly planar preplasma intentionally by sending an uncompressed picosecond-long Ti:sapphire laser pulse with a large spot size onto a thin foil target (Al and mylar) and investigated the characteristics of the preplasma by using a space-time-resolved Nomarski interferometer. In this paper, a simple analytical approach employing the one-dimensional collisional plasma concept was also developed and its result is compared with the experimental results. This work reveals the detailed characteristics of the behavior of the planar preplasma, which is very important in laser-driven proton acceleration, X-ray laser, etc., employing laser-solid interactions. •We produced a nearly planar preplasma by using a large laser spot size on the foil target.•The planar preplasma has a very important advantage because it will provide more stable proton beam energy.•The generated planar plasma characteristics was investigated by a space-time-resolved Nomarski interferometer.•A one-dimensional analytical model based on the collisional plasma concept was developed and compared with the experimental result.•The result will be important for researches in laser-driven proton acceleration, X-ray laser, high energy density physics, etc.