Abstract

Second-order nonlinear optics forms a foundation for generating new coherent sources of light in a broad spectrum of wavelengths by the processes of frequency doubling and mixing. The parametric processes of SHG, SFG, and DFG can be understood as the radiation of coherent light by a nonlinear polarization that oscillates at the second harmonic as well as the sum and difference frequencies of light waves incident on the medium. Frequency doublers and triplers, up-conversion and down-conversion devices, and continuously tunable OPOs have become ubiquitous in optical research laboratories.