ABSTRACT
Harmonic generation can occur in acoustics. In optics, even low-order harmonic generation is useful as it converts two low-frequency photons to a single high-frequency photon. This chapter describes a new type of high-order harmonic generation or high-harmonic generation (HHG). It is nonper-turbative and has a very different generating mechanism from traditional nonlinear optics. HHG is directly responsible for multiple new frontiers in ultrafast phenomena such as attosecond physics. Its impact has far exceeded the original scientific curiosity and rapidly expands into materials science and engineering. Experiments on hydrogen atoms are extremely difficult to carry out, and there have been few comparisons of exact numerical calculations to experimental data. Gaseous atoms have dominated high-harmonic generation for several decades. Only a handful of investigations were on solids in the 1990s before the recent resurgence of studies of solids. In summary, our theoretical investigation represents a beginning of high-harmonic generation in magnets.
