Two-Photon Absorption within the Layered Bi2Te3 Topological Insulators and the Role for Nonlinear Transmittance Therein
In this study, strong two-photon absorption (TPA) in a layered bismuth telluride (Bi2Te3) topological insulator (TI) is observed and investigated by the Z-scan method under the excitation of a femtosecond laser pulse at the wavelength of 1056 nm. The nonlinear transmission measurements reveal that Bi2Te3 possesses not only the property of single photon absorption (SPA) but also the effect of TPA. The saturation TPA coefficient as high as ∼2.29×106 cm/GW has been obtained, which is at least two orders of magnitude higher than other 2D materials, such as MoS2. The large TPA effect in Bi2Te3 TI is attributed to the existence of high-lying bulk states located on the top of the first bulk state. Meanwhile, it can also be used to explain the discontinuity of optical nonlinear transmittance between the low and high excitation energy regions.