Control of energy spectra and enhancement of energy conversion of fast electrons generated by dual-color lasers

Seeking for a high-gain fusion scheme is a hot issue in inertial confinement fusion community, especially after the successful fusion ignition at National Ignition Facility. Fast ignition provides an alternative due to its potential to reduce the energy of driven lasers and achieve higher target gain, whose key step is efficiently generating fast electron beam using picosecond lasers. The properties of the electron beam, such as energy spectra, determine heating efficiency and neutron yield. In this paper, with two-dimensional particle-in-cell simulations, we studied how the dual-color lasers affect the fast electron generation. We find that the energy transfer ratio from laser to fast electrons would significantly increase, and the fast electron energy spectra would be adjusted in the dual-color injecting scheme, where an extra weak low-frequency laser is injected with the main pulse. These phenomena are attributed to the longitudinal electric field modulation in the relatively low-density region and relativistic electromagnetically induced transparency (EIT) process in microchannels formed in the over-dense region. Our results can be applied to fast ignition schemes and applications based on relativistic electron generation with different pulses.