Spin conservation in high-order-harmonic generation using bicircular fields

TL;DR

This paper introduces a new theoretical model for high-order harmonic generation with bicircular fields, demonstrating spin angular momentum conservation at the individual harmonic level, aligning well with experimental data.

Contribution

The paper proposes a novel theoretical approach that explicitly conserves spin angular momentum for each harmonic, differing from previous models and matching experimental observations.

Findings

The model agrees with experimental results on spin conservation.

It accurately describes harmonic generation in both nonperturbative and perturbative regimes.

It shows conservation of spin angular momentum for each harmonic generation event.

Abstract

We present an alternative theoretical model for a recent experiment [A.Fleischer et al., Nature Photon. 8, 543 (2014)] which used bichromatic, counter-rotating high intensity laser pulses to probe the conservation of spin angular momentum in high harmonic generation. We separate elliptical polarizations into independent circular fields with definite angular momentum, instead of using the expectation value of spin for each photon in the conservation equation, and we find good agreement with the experimental results. In our description the generation of each individual harmonic conserves spin angular momentum, in contrast to the model proposed by Fleischer et al. Our model also correctly describes analogous processes in standard perturbative optics.