Sprecher
Beschreibung
Nowadays’ research on laser-driven proton acceleration is focusing on the interaction of relativistic-intensity laser pulses with sub-micrometer targets. With such targets, a variety of acceleration mechanisms can be studied, from the robust TNSA to more advanced schemes that predict better performances in particle energy and beam parameters. The ideal conditions for this type of studies are thin targets and sub-picosecond-long laser pulses with relativistic intensities as high as possible, where the target condition (pre-ionization, pre-expansion) at the time of the interaction plays a fundamental role.
For this reason, a series of experimental campaigns using PHELIX to determine the scaling of proton generation with various parameters like laser energy, laser intensity, or laser temporal contrast have been conducted. In the meantime, the PHELIX laser facility is being improved constantly. For instance, the on-target intensity has been increased by nearly one order of magnitude over the last five years, reaching maximum on-target intensities at about $5\,\times\,10^{20}$ W/cm$^2$ for 200 J pulses.
Our findings show that the temporal contrast of the laser plays a predominant role in efficiently coupling the laser energy into particles. Even at these high intensities, the ASE pedestal of the PHELIX laser pulse is low enough to avoid the buildup of a nanosecond pre-plasma thanks to the front end based on ultrafast parametric amplification. However, the ionization threshold is reached during the rising slope of the pulse, about 100 ps before the maximum of the intensity, which we have identified as the limiting factor for shooting ultra-thin foils. For these PHELIX parameters, record-high maximum proton energies above 90 MeV have been observed with targets about 1 micrometer thick.
In this talk, we will present the most recent results of the last experiments conducted at PHELIX in 2018, putting an emphasis on the characterization of the target state at the very time of the interaction with advanced optical methods. We will also review the current bottlenecks that we are working on, to improve these results even more.
| Working group | Laser-driven ion acceleration |
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