Quantum Optical Description of High-order Harmonic Generation
High-order Harmonic Generation (HHG) is a highly non-linear process in which an atom interacts with a strong laser field. The laser field lowers the atomic potential barrier allowing bound electrons to escape into the continuum through tunnel ionization, propagate, and, with some probability, recombine with the parent ion. As a result, coherent eXtreme UltraViolet (XUV) radiation is emitted in the