Amplification of High Harmonics Using Weak Perturbative High Frequency Radiation

TL;DR

This paper investigates how adding a weak high-frequency XUV seed field to a strong IR laser enhances high-order harmonic generation, combining quantum and semiclassical models to explain the amplification mechanism.

Contribution

It provides a combined quantum-mechanical Floquet and semiclassical analysis to explain the amplification of high harmonics by a weak perturbative high-frequency field.

Findings

High-frequency field induces transitions between Floquet states.

Enhancement arises from time-dependent modulation of the ground state.

New dipole cross terms contribute to harmonic amplification.

Abstract

The mechanism underlying the substantial amplification of the high-order harmonics q \pm 2K (K integer) upon the addition of a weak seed XUV field of harmonic frequency q\omega to a strong IR field of frequency \omega is analyzed in the framework of the quantum-mechanical Floquet formalism and the semiclassical re-collision model. According to the Floquet analysis, the high-frequency field induces transitions between several Floquet states and leads to the appearance of new dipole cross terms. The semiclassical re-collision model suggests that the origin of the enhancement lies in the time-dependent modulation of the ground electronic state induced by the XUV field.