Narrow energy spread proton and ion spectra from high-intensity laser interactions*

Experiments were performed to investigate proton and ion acceleration from thin foil targets, using a high contrast, ultra-short laser pulse from the HERCULES laser at the Univ. of Michigan. Experiments were performed with $30$ TW, $32$ fs pulses after two plasma mirrors with an $F\slash 1$ off-axis parobolic mirror to attain an intensity of $>10^ {21} \; \rm{Wcm}^{-2}$ on $Si_{3}N_{4}$ and Mylar targets of thicknesses ranging 50 nm to 13 $\mu$m with ASE contrast of $10^ {-13}$. Using a short prepulse, proton beams with energy spreads below 75$\% ~\Delta E \slash E$ were observed from all thicknesses, with a maximum energy of 10 MeV and a minimum energy spread of 25$\%$. Similarly narrow energy spreads were observed for O, N, and C ions for $Si_{3}N_{4}$ thickness of 50 nm, with energies up to 2 MeV per nucleon and energy spread of 23$\% $, with energy spread increasing with increased thickness. Maximum energies were confirmed with CR39 track detectors, while a Thomson ion spectrometer was used to measure energy spectra. Two dimensional particle-in-cell simulations were also performed and will be presented.