The effect of laser pulse evolution on down-ramp injection in laser wakefield accelerators.

Electron self-injection in laser wakefield accelerators (LWFAs) is an important determinator of electron beam parameters. Controllable and adjustable LWFA beams are essential for applications. Controlled injection by capturing sheath electrons can be achieved using plasma density down-ramps or bumps, which perturb the LWFA bubble phase velocity by varying the plasma frequency and by affecting relativistic self-focussing of the laser.

Propagation of intense laser pulses in plasma with a prepared phase-space distribution.

Optimizing the laser wakefield accelerator (LWFA) requires control of the intense driving laser pulse and its stable propagation. This is usually challenging because of mode mismatching arising from relativistic self-focusing, which invariably alters the velocity and shape of the laser pulse. Here we show how an intense pre-pulse can prepare the momentum/density phase-space distribution of plasma electrons encountered by a trailing laser pulse to control its propagation.

High-Energy, Short-Duration Bursts of Coherent Terahertz Radiation from an Embedded Plasma Dipole.

Emission of radiation from electrons undergoing plasma oscillations (POs) at the plasma frequency has attracted interest because of the existence of intriguing and non-trivial coupling mechanism between the electrostatic PO and the emitted electromagnetic wave. While broadband emission from plasma waves in inhomogeneous plasma is well known, the underlying physics of narrowband emission at the plasma frequency observed in experiments and in solar radio-bursts is obscure. Here we show that a spatially-localized plasma dipole oscillation (PDO) can be generated when electrons are trapped in a moving train of potential wells produced by the ponderomotive force of two slightly detuned laser pulses that collide in plasma and give rise to a burst of quasi-monochromatic radiation.