Propagation time and nondipole contributions to intraband high-order harmonic generation

Applying the semiclassical model, we identify two connected effects in intraband high-order harmonic generation (HHG): (1) propagation time from the point of emission at the source to the point of detection, and (2) beyond-electric-dipole corrections to the light-matter interaction. These effects inherit information regarding the dispersion and cause specific features in the spectra including even-ordered harmonics in systems with space and time-inversion symmetry. They can for certain experimental geometries be measured free of the dipole background.