Investigation of laser ion acceleration inside irradiated solid targets by neutron spectroscopy

Origins and acceleration directions of accelerated ions inside solid LiF, CH-LiF, and LiF-CH targets irradiated by a $450fs$⁠, $20J$⁠, $1053nm$ laser at an intensity of $3×1018W∕cm2$ have been investigated by neutron spectroscopy. The irradiated targets generate neutrons through the reaction $Li7$ $(p,n)Be7$ between accelerated protons and background $Li7$ ions inside the target. The produced neutron spectra observed from two different observation angles 20° and 120° to the target rear-side normal. From the measured and calculated spectra, by three-dimensional Monte Carlo code, the maximum energy, the total number, and the slope temperature of the accelerated ions are investigated. The results indicate that ions are not only accelerated from the front surface toward the rear surface, but also from the rear surface toward the front surface with comparable maximum energy and higher number.