The major research equipment of the Attosecond Light Pulse Source of the Extreme Light Infrastructure (ELI-ALPS) are driven by laser pulses of few cycle duration operating in the 100 W average power regime. The peak power and the repetition rate span from 1 TW at 100 kHz up to PW at 10 Hz. The systems are designed for stable and reliable operation, yet to deliver pulses with unique parameters, especially with unmatched fluxes and extreme bandwidths. This exceptional performance will enable the generation of secondary sources with exceptional characteristics, including light sources ranging from the THz to the X-ray spectral ranges, and particle sources.
The experimental activities in the building complex to be inaugurated early 2017 will start with the installation of the two 100 kHz repetition rate, CEP stabilized lasers in May 2017. The MIR laser produces 0.15mJ, shorter than 4-optical-cylce pulses tunable between 2.5-3.9 µm. The first stage of the HR laser will provide pulses around 1 µm with 1 mJ energy and pulse duration less than 6.2 fs. The systems will be optically synchronized to each other with a temporal jitter below 1 fs.
Along with the installation of the lasers, we will also start the assembly of the high harmonic beamlines and the THz laboratory, as well as nanoplasmonic experiments. The XUV bursts of light with attosecond duration are expected to be generated by the end of 2017.
Laser-driven particle acceleration has become a growing field of research, in particular for its numerous interesting applications. One of the most common proton acceleration mechanism that is obtained on typically available multi-hundred TW laser systems is based on the irradiation of thin solid metal foils by the intense laser, generating the proton acceleration on its rear target surface. The efficiency of this acceleration scheme strongly depends on the type of target used. Improving the acceleration mechanism, i.e. enhancing parameters such as maximum proton energy, laminarity, efficiency, monocromaticy, and number of accelerated particles, is heavily depending on the laser-to-target absorption, where obviously cheap and easy to implement targets are best candidates. In this work, we present nanostructured targets that are able to increase the absorption of light compared to what can be achieved with a classical solid (non-nanostructured) target and are produced with a method that is much simpler and cheaper than conventional lithographic processes. Several layers of gold nanoparticles were deposited on solid targets (aluminum, Mylar and multiwalled carbon nanotube buckypaper) and allow for an increased photon absorption. This ultimately permits to increase the laser-to-particle energy transfer, and thus to enhance the yield in proton production. Experimental characterization results on the nanostructured films are presented (UV-Vis spectroscopy and AFM), along with preliminary experimental proton spectra obtained at the JLF-TITAN laser facility at LLNL.
Recent theoretical and experimental studies suggest the possibility of enhancing the efficiency and ease of laser acceleration of protons and ions using underdense or near critical plasmas through electrostatic shocks. Very promising results were recently obtained in this regime. In these experiments, a first ns pulse was focused on a thin target to explode it and a second laser with a high intensity was focused on the exploded foil. The delay between two lasers allowed to control the density gradient seen by the second laser pulse. The transition between various laser ion acceleration regimes depending on the density gradient length was studied. With a laser energy of a few Joules, protons with energies close to the energies of TNSA accelerated protons were obtained for various exploded foils configurations. In the high energy regime (~180 J), protons with energies significantly higher than the ones of TNSA accelerated protons were obtained when exploding the foil while keeping a good beam quality. These results demonstrate that low-density targets are promising candidates for an efficient proton source that can be optimized by choosing appropriate plasma conditions. New experiments were also performed in this regime with gas jets. Scaling shock acceleration in the low density regime to ultra high intensities is a challenge as radiation losses and electron positron pair production change the optimization of the shock process. Using large-scale Particle-In-Cell simulations, the transition to this regime in which intense beams of relativistic ions can be produced is investigated.
Energy Energy transfer between a long (3-10 ps) "pump" pulse and a short (400 fs) "seed" one, both at a wavelength of 1.057μm
quasi counterpropagating in an underdense preformed plasma and produced from the ionization of a gas jet, was
observed. Numerical simulations reveal that the energy transfer is due to the coupling involving ion acoustic waves
excited in the Stimulated Brillouin Backscattering in the strong coupling regime. The plasma characteristics were
tailored using a high-energy ionization laser beam and the plasma density was controlled using a Thomson scattering
diagnostic. The energy exchange was observed for different gas (ion) types, pressures (plasma densities), polarization
and intensities of the interacting beams.