Frequency conversion in random nonlinear nanoscale media

Nonlinear optics studies the nonlinear optical response of matter. Nonlinear frequency conversion as one of the most important nonlinear optical phenomena has accompanied the birth and development of nonlinear optics, which still has great research value until now. Nonlinear frequency conversion can be used to realize the extension of coherent light source in all-optical band, because the principle of nonlinear harmonics generation is based on the transition of the virtual energy levels and ground states. Such virtual energy level can be continuously changed, which is not like the real atomic energy level that only has some specific values. Nonlinear frequency conversion has been used to achieve coherent light sources from infrared to submillimeter wave and from vacuum ultraviolet to X-ray. Besides, the study of the interaction between light and nanoscale media led to the birth of nanophotonics, which gradually became the focus of modern optics researches. In this chapter, we will focus on frequency conversion in random nonlinear nanoscale media. In Section 1, we give a brief introduction of optical scattering property, fabrication process, and characterization of such random nonlinear nanoscale media. In Section 2, we introduce the random cavity-enhanced frequency conversion in nonlinear nanoscale media. In Section 3, nonlinear enhancement assisted by external resonance cavity is introduced in case of weak scattering. In Section 4, SH spatial and spectral manipulations are introduced with wavefront control and feedback algorithm in such nonlinear nanoscale media.