Two states hydrogenlike model for High-Order Harmonic Generation and enhanced XUV Generation from a coherent superposition of bound states

TL;DR

This paper develops a quantum theory for high harmonic generation in a two-state hydrogenlike atom model, explaining how coherent superpositions and quantum interference enhance XUV generation efficiency.

Contribution

It introduces an analytic, fully quantum model that accounts for arbitrary potentials, polarization, state depletion, and explains the role of quantum interference in harmonic generation.

Findings

High conversion efficiency is achieved with initial superpositions.

Quantum interference from four electron paths influences the spectrum.

Efficiency depends on initial state amplitudes, depletion, and dipole strengths.

Abstract

We present an analytic, and fully quantum theory of high harmonic generation by low frequency laser fields for a two-state hydrogenlike atom model. The model is valid for an arbitrary atomic potential role of dipole matrix elements and can be generalized to describe laser fields of arbitrary polarization and includes the depletion of states. In the case of an initial coherent superposition of two states, the theory clearly explains why high conversion efficiency can be obtained. Our results are based on quantum interference effects in recombination via different states. We demonstrate that four quantum paths of electron contribute in the harmonic spectrum. The harmonic conversion efficiency is directly proportional to the initial-state amplitudes and depletion of the states (especially excited state), the remained population of the bound states at the time of recombination and the distinct dipole strengths. The main contribution to high conversion efficiency is the transition from the excited to the ground state.