Enhanced laser-driven proton acceleration via improved fast electron heating in a controlled pre-plasma

Abstract

The interaction of ultraintense laser pulses with solids is largely affected by the plasma gradient at the vacuum–solid interface, which modifies the absorption and ultimately, controls the energy distribution function of heated electrons. A micrometer scale-length plasma has been predicted to yield a significant enhancement of the energy and weight of the fast electron population and to play a major role in laser-driven proton acceleration with thin foils. We report on recent experimental results on proton acceleration from laser interaction with foil targets at ultra-relativistic intensities. We show a threefold increase of the proton cut-off energy when a micrometer scale-length pre-plasma is introduced by irradiation with a low energy femtosecond pre-pulse. Our realistic numerical simulations agree with the observed gain of the proton cut-off energy and confirm the role of stochastic heating of fast electrons in the enhancement of the accelerating sheath field.

Effect of the rising edge of ultrashort laser pulse on the target normal sheath acceleration of ions

“…The density profile of ionised targets strongly affects phenomena such as hot electron generation in targets irradiated by the laser pulse [10][11][12] or laser-driven ion acceleration. In the case of ion acceleration, which is the subject of this study, the effects of pulse pedestals or prepulses were broadly investigated in the past [13][14][15][16][17][18][19]. Ion acceleration can be enhanced when the optimal scale length of the preplasma is formed on the laser-irradiated side of the target [15,16,19,20].…”

“…In the case of ion acceleration, which is the subject of this study, the effects of pulse pedestals or prepulses were broadly investigated in the past [13][14][15][16][17][18][19]. Ion acceleration can be enhanced when the optimal scale length of the preplasma is formed on the laser-irradiated side of the target [15,16,19,20]. In contrast, the acceleration can be substantially reduced or even destroyed as a shock wave launched by the rapid surface preheating and/or radiative heating from x-rays generated in the focus of a prepulse incident on the target front side induces a rear surface expansion of thin targets [13][14][15].…”

Novel approach to TNSA enhancement using multi-layered targets—a numerical study

“…On the other hand, the influence of prepulses can also be beneficial for TNSA through the formation of preplasma [17]. The interaction of the main laser pulse with preplasma has been found to enhance laser energy absorption and improve fast electron heating on the front side [30,31], which results in stronger accelerating fields on the rear side. Therefore, it makes sense to design relatively thin TNSA targets that can withstand some level of prepulses while maintaining their structural integrity for the main pulse.…”

Inhibition of electron refluxing in laser-gas interactions for enhanced positron generation

“…For direct laser-solid interactions, the most direct way to increase the positron production is to increase the temperature of the hot electrons. This can be achieved by using low-density pre-formed plasma at the target surface, since this ablated pre-plasma can significantly improve both the laser absorption and fast electron generation [20][21][22]. Other methods, such as using either a Helmholtz coil or curved targets [23,24], have also been proposed to increase the positron density due to the focusing of the positron by an external magnetic field or self-generated fields.…”