Laser harmonic generation in chiral media: a beat-wave approach

In previous studies on laser harmonic generation in plasma and solids, we have developed a beat-wave approach to laser harmonic generation, in which all Fourier spectra take the form of regular grids [1–3]. In this paper, we extend our model to the nonlinear optical response of isotropic chiral media driven by locally chiral light [4–7], in which the tip of the electric-field vector draws a chiral Lissajous figure in time. As in our earlier work on laser-solid interactions [1], the medium is represented by a zero-frequency (DC) driving mode. We show how an enantio-sensitive DC mode can be derived from the interaction of synthetic chiral light with a chiral medium. The beating between this DC mode and the EM fields then leads to a regular harmonic spectrum with alternating chiral and achiral modes. We will derive the criteria for these modes to overlap in Fourier space, so they can combine to yield enantio-sensitive interference patterns or line intensities. Finally, we will apply our framework to a variety of existing results [4–7] to validate its predictions. [1] R. Trines et al., Nature Communications 15, 6878 (2024). [2] R. Trines et al., Proc. SPIE PC13347, PC133470H (2025); https://doi.org/10.1117/12.3043381 [3] R Trines et al., arXiv:2507.08635 (2025). [4] D. Ayuso et al., Nature Photonics 13, 866 (2019). [5] D. Ayuso et al., Nature Communicaitons 12, 3951 (2021). [6] N. Mayer et al., Nature Photonics 18, 1155 (2024). [7] J. Vogwell et al., Science Advances 9, eadj1429 (2023).