Abstract
We apply Fourier-transform spectral interferometry (FTSI) to study the interaction of intense laser pulses with ultrathin targets. Ultrathin submicrometer-thick solid CH targets were shot at the PHELIX laser facility with an intensity in the mid to upper 10^{19} W/cm^{2} range using an innovative double-pulse structure. The transmitted pulse structure was analyzed by FTSI and shows a transition from a relativistic transparency-dominated regime for targets thinner than 500nm to a hole-boring-dominated laser-plasma interaction for thicker targets. The results also confirm that the inevitable preplasma expansion happening during the rising slope of the pulse, a few picoseconds before the maximum of the pulse is reached, cannot be neglected and plays a dominant role in laser-plasma interaction with ultrathin solid targets.
Highlights
In the laboratory, a much more complicated picture emerges from experiments aiming at studying laser-driven ion acceleration, because additional phenomena like the hydrodynamical preexpansion of the target during the rising slope of the laser pulse is a major issue
Ultrathin submicrometer-thick solid CH targets were shot at the PHELIX laser facility with an intensity in the mid to upper 1019 W=cm2 range using an innovative double-pulse structure
The transmitted pulse structure was analyzed by Fourier-transform spectral interferometry (FTSI) and shows a transition from a relativistic transparency-dominated regime for targets thinner than 500 nm to a hole-boring-dominated laser-plasma interaction for thicker targets
Summary
Week ending 23 JUNE 2017 the following that this can be used to characterize the dominating effect in the interaction, namely, laser hole boring or relativistic transparency. We find that, using state-of-the-art temporal contrast optimization equipment, thin submicrometer foils irradiated with PHELIX undergo a significant preplasma expansion happening in the last tens of picoseconds before the maximum of the pulse is reached. Very low group velocities can be expected when the electron density approaches the relativistically corrected critical plasma density, it is experimentally not realistic to observe this effect with state-of-the-art machines. This is due to the submicrometer propagation length at stake combined with the narrow width of this type of resonance. When the plasma is overcritical, the laser pulse pushes the electrons forward because of its ponderomotive force and makes its way inside the plasma at the hole-boring velocity vh [15], sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi vh 1⁄4 c
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