Production of 25 MeV Protons in CO2 Laser-Plasma Interactions in a Gas Jet

At the Neptune Laboratory at UCLA, we have developed a high-power CO2 MOPA laser system which produces world record, multi-terawatt 10μm pulses. The CO2 laser pulses consist of a train of 3ps pulses separated by 18ps, each with a peak power of up to 4TW and a total pulse train energy of ∼100J. These relativistic laser pulses are used for Laser Driven Ion Acceleration in a H2 gas jet operated around the critical density of 1019cm−3 for 10μm. The laser is focused into the gas jet reaching a normalized field strength of ao∼2 in vacuum. For these conditions, protons with a maximum energy of 25MeV and a narrow energy spread of ΔE/E∼1% are recorded. Initial analysis of these experimental results shows a stronger scaling of the proton energy than that predicted from the ponderomotive force, and highlights the importance of an accumulated effect of multiple CO2 laser pulses lasting over 100ps. The temporal dynamics of the overdense plasma slab are probed with a picosecond 532nm pulse and the results will be discussed.