Third-order Nonlinear Effect Therory Research Of Antiferromagnetic Systems

The resonant frequencies of antiferromagnetic(AF) material lie in the Tera-hertz(THz) frequency region, so the investigation of the AF nonlinearity is valuble for the expansion of communication frequency. However,the AF nonlinearity is very weak, which needs a very strong electromagnetic wave (or strong light) to illuminate. Therefore, enhance the nonlinear effectd of AF is use-ful primarily for application. The optical bistability (OB), and the nonlinear transmission through and reflection of an AF film and AF photonic crystal have been investigated with the AF nonlinear theory in this study. The innovations of this work are listed as follows:1. With the external magnetic field, the third-order nonlinear susceptibility are obtained from the dynamical equation in a uniaxial antiferromagnet with two sublattices, such as MnF2 , FeF2. The analytical expressions of them establish a solid foundation for discussing other nonlinear phenomena of AF.2. The OB of the AF film, which is one of the third-order nonlinear effects, is studied in the Voigt geometry. The results show that the properties of OB near the higher and lower resonant frequencies are completely different. Especially, only in the higher resonant frequencies region, the OB can be observed at H0=1.0kG. But when the external magnetic field is increased to 2.0kG, the OB can lie in the two resonant frequencies. The OB can be modulated through chang-ing the incident angle, the thickness and the external magnetic field.3. We calculate the OB of a one-dimension photonic crystal embedded an AF film in the Voigt geometry. According to the theory of the electromagnetic wave localization, the third-order nonlinear effect can be enhanced. The results show that the OB can be detection near the two resonant frequencies when the incident angle is small. However, in the larger incident angle region, also only increasing the magnetic field strength we can observe the OB near the lower resonant frequecy. Also, the OB effect can be further modulated through chang-ing the number of dielectric medium.4. We present a theory of nonlinear infrared transmission through and reflec-tion off an AF film. The spread of electromagnetic wave in AF can be character- ized by the properties of the nonlinear transmission and reflection. Two cases are calculated: an AF film is put in the vaccum; an AF film is put into different di-electrics. In the two geometries, we see the discontinuities on the reflection and transmission curves, and the nonlinear effect is very obvious near to the jump points. The nonlinear interation also plays an important role in decreasing or in-creasing the absorption in the AF film.