Efficient forward direct laser acceleration of electrons in subcritical plasma with injection through hybrid parametric instability

Efficient forward electron acceleration by the direct laser acceleration (DLA) in the plasma channel was experimentally demonstrated using a 16 µm thick tape target. An electron beam with ∼0.05 rad divergence, 50-100 pC charge (for E<1.7 MeV), and temperature ∼ several MeV was observed on 1 TW laser system utilizing an additional controlled nanosecond prepulse. Using this beam, several near-threshold photonuclear reactions were studied and neutron flux of ∼ 105 − 106 s-1 J-1 was achieved. We also used neutron flux measurements to estimate electron beam charge, calculating conversion coefficients from GEANT4 simulations. Terahertz radiation emission from this type of interaction was also studied, exhibiting a two-maxima structure with the change of delay between main pulse and nanosecond prepulse.