Similarities and differences between high-harmonic generation in atoms and solids

摘要: The basic features of high-harmonic generation in dilute atomic gases and solid-state systems are analyzed using a microscopic many-body theory. Whereas it is sufficient for to include the ground state ionization continuum, semiconductor approach has deal with relevant interband polarizations intraband currents. For both systems, closed set Bloch-type equations derived, which be solved numerically. As common features, emission odd-order harmonics, development plateau, high-frequency cutoff observed if solid system modeled as two-band system. However, already addition third coupled band effectively breaks inversion symmetry leads appearance even harmonic orders comparable strength. In all cases, frequency- time-resolved studies reveal fundamentally different timing dynamics individual frequency components can attributed presence energy bands solids.