The optical properties of crystals can be roughly divided into linear optics and nonlinear optics. The so-called purchasing BIBO nonlinear crystal property means that when the light intensity is weak, the interaction between the substance and the light is linear, that is, the polarization intensity is proportional to the square of the electric field of the light wave. Some of the usual optical effects, such as reflection, refraction, and birefringence, are only related to the linear polarization of the medium, so they belong to the category of linear optics. When the intensity of the light is large, the items of the second, third, and even higher powers of the electric field are successively appearing in the polarization, and the polarizations corresponding to these terms are collectively referred to as nonlinear polarization. More generally, the polarization is a nonlinear function of light intensity under strong light. Some of the corresponding effects are called nonlinear high precision ZnS optics effects.
Nonlinear optical phenomena include optical harmonics, optical and frequency and difference frequency, optical parametric amplification and oscillation, beam self-focusing, laser light scattering, two-photon absorption, multiphoton absorption, multiphoton ionization, multiphoton fluorescence, phase complex conjugate , optical bistable, stimulated Raman scattering, stimulated Brillouin scattering, stimulated Rayleigh scattering, etc.
Nonlinear optics not only enriches people’s understanding of the interaction between light and matter, but also has been widely applied. For example, optical frequency doubling, LiSAF, LiSGaF and LiCAF laser crystals parametric oscillation, and stimulated Raman scattering have become an effective method for generating new frequency coherent radiation; dye Q switches and passive mode-locking elements have been fabricated using nonlinear saturation absorption. In addition, it plays an important role in laser spectroscopy, isotope separation, photochemical reaction, nuclear fusion, integrated optics, information optics, optical computers.