Understanding the role of relaxation in high harmonic generation

A central challenge in simulations of high-harmonic generation (HHG) is the accurate treatment of intraband relaxation (depopulation) and interband relaxation (dephasing). Although commonly introduced as empirical parameters, these processes exert a significant influence on the computed spectra and are often required to obtain reasonable agreement with experiment. In this work, we study their impact by incorporating state-dependent lifetimes arising from electron–phonon interactions into ab initio HHG calculations. Using a typical 2D material, monolayer MoS2, we demonstrate that state-dependent lifetimes substantially reshape the HHG spectrum, modifying the relative harmonic intensities and cutoff behavior. Our findings elucidate the role of phonon-induced relaxation in HHG and advance efforts toward parameter-free, predictive simulations of strong-field phenomena in solids.