Macroscopic simulation of near-threshold high harmonic generation using microscopic TDSE calculations

Modeling strong-field induced radiation near the ionization threshold requires careful treatment of excited state dynamics. Solution of the time dependent Schrodinger equation (TDSE) provides accurate data in this regime, but the computational time needed prohibits direct calculation of the macroscopic response (e.g., from a gas jet) due to the range of intensities to be considered. We apply a method of interpolation of (precalculated) TDSE results as a function of laser intensity at a given wavelength to simulate the macroscopic propagation of the high harmonic signals using the discrete dipole approximation. This allows investigation of the angular dependence of harmonic and off-harmonic radiation near and below the ionization threshold. Results for hydrogen and helium will be presented.