45. Effects of prepulses on laser-driven ion acceleration

Plasma produced by high-intensity lasers can generate quasistatic electric fields capable of accelerating ions to MeV energies over micron-scale distances. In a typical experiment, a solid or liquid target is irradiated by an ultrashort laser pulse with an intensity that vastly exceeds the ionization threshold of any material, heating electrons to relativistic velocities.
One of the main challenges in using ultrashort pulses for ion acceleration is the presence of a laser pedestal and/or short prepulses preceding the main pulse. The nanosecond pedestal and femtosecond prepulses can pre-ionize and even destroy thin targets before the main pulse interacts with them. Various methods exist to reduce the intensity of these prepulses and increase the laser pulse contrast (the ratio of peak laser pulse intensity to prepulse intensity). However, achieving a prepulse intensity below the ionization threshold—which can be ten orders of magnitude lower than the main pulse intensity—is highly challenging. As a result, even with an ultrahigh laser contrast, the target may be partially ionized and evaporated before the main pulse, leading to the formation of preplasma. Additionally, rear-side plasma (or skirt) can develop behind the target, significantly reducing the efficiency of laser-driven ion acceleration.
Interpreting experimental results on ion acceleration with finite laser pulse contrast is particularly difficult. The target state before the main pulse arrival can only be measured with limited spatial and temporal resolution, making it insufficient for a detailed interpretation of results. Supporting numerical simulations can provide deeper insights, but different computational approaches are required to fully describe the interaction.
The main goal of this thesis is to integrate experimental and theoretical efforts to better understand laser-driven ion acceleration with finite-contrast laser pulses. In the first phase, hydrodynamic simulations (using the FLASH code) or particle-in-cell (PIC) simulations (using the SMILEI code) will be performed to study the underlying physics. For a more advanced and extensive study (e.g., a PhD thesis), the work will include experimental preparation and participation in relevant experiments.