Electron, photon, and ion beams from the relativistic interaction of Petawatt laser pulses with solid targets

Abstract

In our Petawatt laser experiments several hundred joules of 1 µm laser light in 0.5-5.0 ps pulses with intensities up to 3x10 20 Wcm -2 were incident on solid targets producing a strongly relativistic interaction. The energy content, spectra, and angular patterns of the photon, electron, and ion radiations were diagnosed in a number of ways, including several novel (to laser physics) nuclear activation techniques. From the beamed bremsstrahlung we infer that about 40-50% of the laser energy is converted to broadly beamed hot electrons. Their direction centroid varies from shot to shot, but the beam has a consistent width. Extraordinarily luminous ion beams almost precisely normal to the rear of various targets are seen -up to 3x10 13 protons with kT ion ~ several MeV representing ~6% of the laser energy.We observe ion energies up to at least 55 MeV. The ions appear to originate from the rear target surfaces.The edge of the ion beam is very sharp, and collimation increases with ion energy. At the highest energies, a narrow feature appears in the ion spectra, and the apparent size of the emitting spot is smaller than the full back surface area. Any ion emission from the front of the targets is much less than from the rear and is not sharply beamed. The hot electrons generate a Debye sheath with electrostatic fields of order MV per micron which apparently accelerate the ions.

Envelope model for passive magnetic focusing of an intense proton or ion beam propagating through thin foils

“…This should aid both carrying out higher detail simulations and design of proof-of-principle experiments to enable applications in both ion and proton beam focusing to a small spot for targets and for beam collimation for injection in an accelerator. Short pulse laser-illuminated foils produce proton beams with very low emittances, high enough energy, and high spacecharge intensity [24][25][26][27]. Such proton beams provide an opportunity to test passive foil focusing on existing laboratory systems.…”

Investigations of Field Dynamics in Laser Plasmas with Proton Imaging

“…If the laser light interacts with the target electrons and x-rays are produced apart from energetic ions [58]. Since the MCP is also sensitive to these signals, the recorded images would be strongly influenced by them and not analyzable.…”

“…A nearly exponential dependence of the maximum field and the laser energy is indicated. Regarding to the scaling laws given in reference [58] for the TNSA-process and the laser energy conversion [91] one would expect a dependence of the electric field (E 0,el ) as follows:…”

“…The dependence on the square root of the pulse energy is indicated in Fig. 9.4 and fits with theoretical scaling laws [58]. The low time resolution in the experiments prevent further statements about the temporal evolution of the fields.…”

The ELIMED transport and dosimetry beamline for laser-driven ion beams

“…Since the first experiments on laser-matter interaction, wide theoretical and experimental progresses have been carried out, confirming the possibility to accelerate multi-MeV ion beams from the interaction of high-intensity laser pulses (from 1018 to 1020 W/cm2) on thin solid targets [3][4][5]. So far different acceleration regimes [6][7][8][9][10][11], such as the Target Normal Sheath Acceleration (TNSA) [12][13][14], the Radiation Pressure Acceleration (RPA) [15][16][17] and the Break-Out Afterburner (BOA) [18], have been studied and several experimental results, obtained mainly within the TNSA regime, have been reported in the literature [12][13][14]. Some of the peculiarities of the accelerated protons might be of interest for different kind of applications, including the medical ones.…”