Modelling intensity volume averaging in ab initio calculations of high harmonic generation

• Published in: Journal of physics. B, Atomic, molecular, and optical physics Vol. 56; no. 13; pp. 135402 - 135411
• Main Authors: Hutcheson, L, van der Hart, H W, Brown, A C
• Format: Journal Article
• Language: English
• Published: IOP Publishing 14.07.2023
• Subjects: calculations; focal volume averaging; high harmonic generation
• ISSN: 0953-4075; 1361-6455
• DOI: 10.1088/1361-6455/acda6f

Abstract We present an approach to assess the survival of single-atom effects in the macroscopic high-harmonic generation (HHG) spectrum, by accounting for focal volume averaging. We apply this technique to R-matrix with time-dependence (RMT) studies, which are designed to include the full multielectron response of an atom. Such an approach allows the assessment of which features of an experimentally-measured HHG spectrum of diffuse gases may be traced directly to single-atom effects and vice-versa. While accounting for the phase of harmonics produced at different locations in the focal volume gives the most accurate results, a simplified approach, using a smaller number of RMT calculations, is found to provide comparable conclusions. We apply these approaches to compute intensity-averaged harmonic spectra in two different experimental regimes.