Nonlinear optical materials refer to materials whose optical properties depend on the intensity of incident light. Nonlinear optical properties are also called optical properties under the action of strong light, mainly because these properties are only manifested under the action of strong coherent light such as lasers.
1. Inorganic nonlinear optical materials
In the application of quadratic nonlinear optical materials, inorganic materials have been in the main position for a long time, have made great progress, and have been applied in many devices. Inorganic materials are generally more stable than organic materials, many of them allow anisotropic ion exchange, making them useful for wave guide materials, and they all have crystalline forms that are more pure than organic materials. These include KTP (KTiO2PO4) type materials, KDP (KH2PO4) type materials, perovskite type (LiNbO3, KNbO3, etc.) materials, semiconductor materials (Te, Ag3AsS3, CdSe, etc.), borate series materials (including KB5, BBO, LBO and KBBF), etc., as well as zeolite molecular sieve-based materials, glass-type and complex-type materials.
2. Organic nonlinear optical materials
In the early stage of nonlinear optical materials research, a series of organic compounds such as urea, picric acid, and dinitroaniline were found to have nonlinear optical effects. Since organic molecules with large delocalized π-conjugated electron systems have strong optoelectronic coupling characteristics, high response values and relatively large optical coefficients can be obtained.
After the 1980s, organic nonlinear optical materials developed rapidly. Compared with inorganic materials, organic materials have the advantages of high nonlinear optical coefficient, fast response, easy modification, high optical damage threshold, easy processing and strong molecular variability. Many organic nonlinear optical materials have been discovered or synthesized, including various organic low molecular nonlinear optical materials, high polymer nonlinear optical materials, and metal-organic complex nonlinear optical materials.
3. Metal-organic complex nonlinear optical materials
Mainly include metallocene complexes, metal carbonyl complexes, metal olefin organic complexes, metal polyacetylene polymers, metal porphyrin organic complexes, metal phthalocyanine organic complexes and other complex nonlinear optical materials, etc. . Due to the diversity of ligands and metals, metal-organic compounds also have various structures, which have more advantages than nonlinear optical materials composed of simple organic molecules.
4. Inorganic/Organic Hybrid Materials
Inorganic//organic hybrid nonlinear optical materials combine the advantages of inorganic materials and organic materials, and incorporate organic functional molecules or polymers into inorganic networks through methods such as salt formation or sol/gel technology. A new class of materials that form chemical bonds between them.
Through the rigid amorphous two-dimensional structure and excellent high temperature stability of inorganic glass, the orientation relaxation of chromophores can be suppressed, and the thermal stability of the material can be improved. In addition, it has good film-forming properties and is a class of materials with good application prospects. Nano-doped microcrystalline semiconductor glass is the most widely used third-order nonlinear optical material.