RESUMEN
We introduce a novel, gaseous target optical shaping laser set-up, capable to generate short scale length, near-critical target profiles via generated colliding blast waves. These profiles are capable to maintain their compressed density for several nanoseconds, being therefore ideal for laser-plasma particle acceleration experiments in the near critical density plasma regime. Our proposed method overcomes the laser-target synchronization limitations and delivers energetic protons, during the temporal evolution of the optically shaped profile, in a time window of approximately 2.5 ns. The optical shaping of the gas-jet profiles is optimised by MagnetoHydroDynamic simulations. 3D Particle-In-Cell models, adopting the spatiotemporal profile, simulate the 45 TW femtosecond laser plasma interaction to demonstrate the feasibility of the proposed proton acceleration set-up. The optical shaping of gas-jets is performed by multiple, nanosecond laser pulse generated blastwaves. This process results in steep gradient, short scale length plasma profiles, in the near critical density regime allowing operation at high repetition rates. Notably, the Magnetic Vortex Acceleration mechanism exhibits high efficiency in coupling the laser energy into the plasma in the optically shaped targets, resulting to collimated proton beams of energies up to 14 MeV.
RESUMEN
Laser WakeField Acceleration (LWFA) is extensively used as a high-energy electron source, with electrons achieving energies up to the GeV level. The produced electron beam characteristics depend strongly on the gas density profile. When the gaseous target is a gas jet, the gas density profile is affected by parameters, such as the nozzle geometry, the gas used, and the backing pressure applied to the gas valve. An electron source based on the LWFA mechanism has recently been developed at the Institute of Plasma Physics and Lasers. To improve controllability over the electron source, we developed a set of 3D-printed nozzles suitable for creating different gas density profiles according to the experimental necessities. Here, we present a study of the design, manufacturing, evaluation, and performance of a 3D-printed nozzle intended for LWFA experiments.
RESUMEN
The temporal rearrangement of the spectral components of an ultrafast and intense laser pulse, i.e., the chirp of the pulse, offers significant possibilities for controlling its interaction with matter and plasma. In the propagation of ultra-strong laser pulses within the self-induced plasma, laser pulse chirp can play a major role in the dynamics of wakefield and plasma bubble formation, as well as in the electron injection and related electron acceleration. Here, we experimentally demonstrate the control of the generation efficiency of a relativistic electron beam, with respect to maximum electron energy and current, by accurately varying the chirp value of a multi-10-TW laser pulse. We explicitly show that positively chirped laser pulses, i.e., pulses with instantaneous frequency increasing with time, accelerate electrons in the order of 100 MeV much more efficiently in comparison to unchirped or negatively chirped pulses. Corresponding Particle-In-Cell simulations strongly support the experimental results, depicting a smoother plasma bubble density distribution and electron injection conditions that favor the maximum acceleration of the electron beam, when positively chirped laser pulses are used. Our results, aside from extending the validity of similar studies reported for PW laser pulses, provide the ground for understanding the subtle dynamics of an efficient plasma electron accelerator driven by chirped laser pulses.