Investigation Of Nonlinear Refractive Effect In Topological Insulator At 800nm

Third-order nonlinear optical effect and its application is the hotspot of research on nonlinear optics. With the deeper study of third order nonlinear optical effect such as nonlinear optical absorption and optical Kerr effect, higher requirement s are put forward for third-order nonlinear optical materials.In recent years, topological insulator has become a hot research t opic in the field of condensed matter physi cs. Topological insulator is di fferent from the conventional insulation and metal. Because of the band inversion caused by strong spin orbit coupling, topological insulator is insulated in the body, but its surface or edge has metallic properties. In the field of condensed matter physics topological insulator has caused the wide attention of the researchers, but the explor ation of optoelectroni cs and nonlinear optical properties is very little. T he focus of thi s article is on the nonlinear refraction property of topological insulators excited by a femtosecond pulse laser at the wavelength of 800 nm. Samples are investigated by transmission Z-scan and reflection Z-scan methods. T he main results of our works are as follows:Experimental study on the third-order nonlinear optical properties of carbon disulfide is used to verify the validity of the Z-scan system. Base on the Coherent company’s titanium doped sapphire solid laser system, combined with the electric translational platform, power probe and power meter, we set up a Z-can experimental platform. T hird-order nonlinear optical properties of carbon disulfide, have been measured by our Z-scan system, and we figured out that the third-order nonlinear refractive index is quite closed to the reported data. T he above experimental results prove that our measurem ent system is stable and reliable.Thin films of topological insulator which are excited by a femtosecond pulse laser at the wavelengt h of 800 nm have been investigated. Transmission Z-scan experimental system i s used to measure the samples. We get the opt ical constants of the sample by fitting experimental data.We study the nonlinear optical property of topological insulator crystal whi ch is excited by a femtosecond pulse laser at the wavelength of 800 nm. T he sample is measured by refl ection Z-scan experimental system. By fitting normalized curve with the formula, nonlinear refractive coeffici ent of Bi 2Te3 and Bi2Se3 crystalis achieved. Furthermore, we analyze the internal competition mechanism of nonlinear effect in materials. Results show that Bi 2Te3 and Bi2Se3 crystals bot h have strong nonlinear refraction effect, and the saturable absorption has great influence on the nonlinear refraction.Experimental results prove that topological insulators have a large nonlinear refractive index at 800 nm which is of great prospects in the manufacture and application of optical devi ces.