Generation of fast highly charged ions in laser–plasma interaction

The nonthermal and nonlinear coupling of strong laser light wave with plasma transfers a part of laser energy into hot electrons and fast ions. The efficiency of these effects depends on the characteristics of a laser pulse, target properties and irradiation geometry. The reported studies were performed with the use of a high-power and high-energy iodine PALS laser system (energy up to 1 kJ in a 0.4 ns pulse at wavelength of 1315 nm and energy up to 250 J at wavelength of 438 nm). The properties of the laser-produced ion streams were determined with the use of ion diagnostics based on the time-of-flight method. The characteristics of x-rays were measured using various semiconductor detectors. The main ion stream characteristics as well as the ion acceleration processes in plasmas of different Z numbers were studied in dependence on laser pulse parameters. The parameters of a fast ion group depend evidently on Z number of the ions. The influence of the electron density scale length on fast ion generation was investigated using a low intensity laser pre-pulses to generate preformed plasmas (pre-plasmas) with which the main laser pulse interacted. The obtained results suggest that ion acceleration processes were most effective at a specific electron density gradient scale length of pre-plasma determined by the pre-pulse parameters.