Quasi-phase-matching of high-order-harmonic generation using multimode polarization beating

TL;DR

This paper explores a novel method for high-order harmonic generation using multimode polarization beating to achieve quasi-phase-matching, enhancing efficiency through phase modulation rather than amplitude modulation.

Contribution

It introduces a generalized approach to quasi-phase-matching via polarization beating in multimode waveguides, demonstrating improved efficiency and providing a Fourier-based analysis of the process.

Findings

Multimode polarization beating can achieve quasi-phase-matching for high-order harmonics.

Phase modulation dominates over amplitude modulation in MMQPM efficiency.

Optimal experimental conditions for implementing this scheme are identified.

Abstract

The generalization of quasi-phase-matching using polarization beating and of multimode quasi-phase-matching (MMQPM) for the generation of high-order harmonics is explored, and a method for achieving polarization beating is proposed. If two (and in principle more) modes of a waveguide are excited, modulation of the intensity, phase, and/or polarization of the guided radiation will be achieved. By appropriately matching the period of this modulation to the coherence length, quasi-phase-matching of high-order-harmonic radiation generated by the guided wave can occur. We show that it is possible to achieve efficiencies with multimode quasi-phase-matching greater than the ideal square wave modulation. We present a Fourier treatment of QPM and use this to show that phase modulation, rather than amplitude modulation, plays the dominant role in the case of MMQPM. The experimental parameters and optimal conditions for this scheme are explored.