Laser-Driven Proton Acceleration with Water Droplets and Thin Foils at JETI40 and POLARIS

Laser-driven ion acceleration is a complicated process that depends on the laser’s parameters, such as intensity, angle of incidence and the temporal intensity contrast as well as different target parameters, including the target geometry. This talk gives an overview of three experiments carried out in recent years at the Institute of Optics and Quantumelectronics and the Helmholtz-Institute Jena investigating laser-driven ion acceleration with contrast enhanced laser pulses and thin foil targets as well as water micro droplets. In an experiment at the JETI 40 laser system we investigated ion acceleration with water droplets that are available at high repetition rates. By frequency doubling the main laser pulses and using an optical probe at off-harmonic wavelengths, we were able to obtain high-quality images of the laser droplet interaction on a picosecond timescale. With the help of these images, we were able to study not only the influence of the angle of incidence on the proton acceleration process, but also the influence of an additional pre-impulse. At the POLARIS laser system, frequency-doubled laser pulses and submicron plastic foils were used to investigate the characteristics and the origin of a ring-like profile in the protons’ angular distribution. With the help of two-dimensional particle-in-cell simulations, this beam profile could be explained within the established Target Normal Sheath Acceleration model. Finally, recent results from an experiment with a plasma mirror and ultra-thin diamond-like-carbon foils, conducted at POLARIS, will be presented.