Effects of nanosecond-scale prepulse on generation of high-energy protons in target normal sheath acceleration

Abstract

A pulse cleaner based on noncollinear optical-parametric amplification and second-harmonic generation processes is used to improve the contrast of a laser of peak intensity ∼2 × 1019 W/cm2 to ∼1011 at 100 ps before the peak of the main pulse. A 7 MeV proton beam is observed when a 2.5 μm-thick Al foil is irradiated by this high-contrast laser. The maximum proton energy decreases to 2.9 MeV when a low-contrast (∼108) laser is used. Two-dimensional particle-in-cell simulations combined with MULTI simulations show that the maximum proton energy sensitively relies on the detecting direction. The ns-time-scale prepulse can bend a thin target before the main pulse arrives, which reduces maximum proton energy in the target normal sheath acceleration.

Cascaded target normal sheath acceleration

“…[31][32][33][34][35][36][37][38][39] We expect that using the maximum sheath field to accelerate the center of the proton beam is the optimum condition for the cascaded TNSA scheme. In this case, the incident proton beam is largely accelerated and the beam spectrum is simultaneously improved.…”

Identifying the source of super-high energetic electrons in the presence of pre-plasma in laser–matter interaction at relativistic intensities

“…In a real situation, the counter-propagating laser can be produced automatically during the propagation of an intense laser pulse in the plasma through processes such as stimulated Raman backscattering or reflected laser fields from high density regions. However, recently fast electron generation due to relativistic intensity laser-matter interaction influenced by preformed plasma has been addressed in a number of experimental and theoretical studies [21][22][23][24][25][26][27][28], suggesting that the presence of pre-plasma can significantly affect fast electron distributions. The new foundings in experimental and theoretical studies, addressing the influences of pre-plasmas, seem beyond the interpretations of stochastic heating and acceleration models.…”

Ion motion effects on the generation of short-cycle relativistic laser pulses during radiation pressure acceleration

“…In fact, the effect of a laser prepulse is always critical for a thin foil and it may alter the conditions [see Equations (3) and (4)]. A density gradient at the front or back side of the foil produced by the prepulse must be considered if the laser contrast is not ultra-high [9,10] ; such a condition is not considered in this work.…”

“…These events jeopardize the relativistic interaction of the ultra-thin target. Thus, high-contrast [9][10][11][12][13][14][15][16][17][18][19][20] and short-duration laser pulses [21,22] are needed. Plasma mirrors may be a feasible method by which to solve these problems.…”

“…However, prepulses or laser pulses with slowly increasing fronts may lead to premature ionization of the target, and significant expansion of the plasma sheet occurs before the amplitude peak of the pulse arrives [9,10] . These events jeopardize the relativistic interaction of the ultra-thin target.…”