Coherent light sources and optical techniques for Thomson scattering and Laser-Plasma experiments

Recent progress in accelerators and lasers technology opens new perspectives in terms of particle-photon colliders luminosity: low cross section processes can be therefore utilized to create specific radiation sources. Indeed, exploiting the inverse Compton scattering or Thomson back-scattering process, the interaction between relativistic electron beams (γ >> 1) and near-infrared laser pulses (λ ≈ 1μm) yields electromagnetic waves in the X-ray and γ-ray range. The energy, the flux and the spectrum of such kind of generated radiation are suitable for many purposes, e.g. dynamical studies and imaging of solid, molecular and biological systems. Nevertheless, the big development in the high power laser field, begun in the ’80s thanks to the chirped pulse amplification (CPA) scheme [66], has provided systems to be employed in the study of the laser wakefield acceleration (LWFA). As stated by Tajima and Dawson in 1979, an intense laser pulse, propagating through a plasma, can stimulate plasma waves able to accelerate electrons with accelerating gradients greater than 100 GV/m, i.e. some orders of magnitude more than the conventional RF-based LINAC. Moreover, with TW-class laser systems and intensity more than 10^18 W/cm^2, the relativistic regime occurs and electrons can be self-injected into the plasma accelerating structure. This opens the possibility to build much more compact particle accelerators, even though the beam quality, in terms of emittance and energy spread, is not yet comparable to the standard linear accelerator. In this work, the activity related to Thomson back-scattering and laser-plasma interaction pursued at SPARC_LAB Facility in Frascati (Italy) will be presented. SPARC_LAB (Sources for Plasma Accelerators and Radiation Compton with Lasers and Beams) is a multi-disciplinary facility aiming to test new radiation source (THz, XUV, X-Ray) exploiting different phenomena such Free Electron Laser (FEL), Coherent Transition Radiation (CTR) and Thomson back-scattering, thank to the high brightness electron beam that it can provide. The peculiarity of SPARC_LAB is the presence of 300 TW FLAME laser together with the high brightness LINAC. This kind of laser represents a powerful tool to study Thomson back-scattering, when combining it with the linear accelerator, as well as the interaction with the matter, mainly to perform experiments related to LWFA, both in self-injection and external-injection regime. Furthermore, a development of a new diagnostics tool able to measure electron beam emittance in a single shot way will be presented. This novel technique seems to be very useful for beam from plasma accelerators, since they suffer shot-by-shot instabilities. Therefore, a statistical measurement would me meaningless while a single shot diagnostics can provide a more useful description of electron beam parameters. Simulations and some preliminary results will be provided. In addiction, also a research activity on interaction with solid target has been conducted in order to study the possibility to optimize the ion acceleration without increasing the laser energy but opportunely shaping the target itself.