Subfemtosecond Wakefield Injector and Accelerator Based on an Undulating Plasma Bubble Controlled by a Laser Phase

We demonstrate that a long-propagating plasma bubble executing undulatory motion can be produced in the wake of two copropagating laser pulses: a near-single-cycle injector and a multicycle driver. When the undulation amplitude exceeds the analytically derived threshold, highly localized injections of plasma electrons into the bubble are followed by their long-distance acceleration. While the locations of the injection regions are controlled by the carrier-envelope phase (CEP) of the injector pulse, the monoenergetic spectrum of the accelerated subfemtosecond high-charge electron bunches is shown to be nearly CEP independent.