Enhancing high-order harmonic generation by controlling the diffusion of the electron wavepacket

We present a substantial enhancement of the vacuum-ultraviolet photon flux using high-order harmonic generation (HHG) driven by two-color, $\omega$--3$\omega$, laser pulses compared to the fundamental ω driving pulse. Specifically, we achieve over an order-of-magnitude enhancement for 20- to 40-eV photons and up to three-orders of magnitude at lower energies. More importantly, we demonstrate that the $\omega$--3$\omega$ driving field can be used to control the diffusion (also known as "dispersion") of the electron wavepacket. Furthermore, the two-color phase controls the electron excursion time over a factor of two range, enabling one to probe the remaining target at different times. Finally, we show that the divergence angle of the harmonics is reduced by a factor of two, showing that the bichromatic driving fields improve HHG's capability as a light source.