Direct laser acceleration of electrons in a plasma bubble by a tightly confined laser pulse.

Direct laser acceleration (DLA) in a plasma bubble presents a unique opportunity to manipulate the transverse and longitudinal phase spaces of the electron beam propagating inside a plasma bubble. We present an analytical theory and supporting PIC simulations that illustrate several overlooked effects in DLA. A small but finite longitudinal electric field of the laser pulse will be shown to produce a significant deceleration effect that partially offsets the acceleration by its transverse component. It is also shown that the DLA effect is not confined to moderate-energy electrons, but can be extended to GeV-scale beams. Finally, we show that DLA exists even in the decelerating portion of the plasma bubble. Applications of the DLA to X-ray generation and to the enhancement of the transformer ratio of a plasma wakefield accelerator will be discussed, and the results of the full PIC and a novel quasi-static code will be presented.