Enhancing the high-order harmonic generation yield within a specified spectral window via electron wave-packet engineering

A method is proposed to engineer the continuum fraction of the electron wave packet in high-order harmonic generation (HHG) such that a quasi-monochromatic recollision with the atomic core is rendered possible even for parts of the wave packet that were launched to the continuum at different laser phases. Because of this, the HHG spectrum is shown to be enhanced in a specified controllable spectral window. The electron wave-packet engineering is achieved via driving HHG by the combined fields of weak x rays and a strong shaped pulse of infrared radiation. Our calculations based on the strong field approximation show how the enhanced spectral window can be controlled by the shaping of the driving infrared pulse. The scheme is illustrated via a semiclassical trajectory-based analysis