Enhanced photon deceleration in an electron beam-assisted laser wakefield accelerator

The photon deceleration when an ultrashort and ultraintense laser pulse propagates in a underdense plasma can produce intense infrared or THz radiation. We study the frequency of the decelerated photons using an analytical model and find that it is dominated by the residual plasma electron density inside the plasma wake. We thus propose using an assist electron beam to evacuate the plasma electrons in a laser-driven plasma wake and further improve the corresponding refractive index. High-dimensional particle-in-cell simulations demonstrate that relativistic radiation pulses with a frequency of ∼10 THz can be generated in this electron beam-assisted photon deceleration using a 1-μm drive laser. It significantly extends the frequency range of the photon deceleration scheme, which could open up new possibilities for strong terahertz optics.