Nonlinear Optical\nProperties of the Topological Material\nBi<sub>2</sub>Se<sub>3</sub> Family for the Application of an Ultrafast\nPulse Laser Based on the Occupied and Unoccupied Band Structures

The Bi<sub>2</sub>Se<sub>3</sub> family can exhibit many\nintriguing\ntopological insulator properties, including a narrow bandgap and strong\nsurface states, which show excellent nonlinear optical properties.\nThinning bulk Bi<sub>2</sub>Se<sub>3</sub> family materials to create\na low-cost photoelectric modulation device and explaining the mechanisms\nof nonlinear optical differences in different types of materials remain\nchallenges. Based on liquid-phase exfoliation technology and tapered\nfiber, this work prepared optoelectronic modulation devices for various\nsamples within the Bi<sub>2</sub>Se<sub>3</sub> family, quantitatively\ncompared their nonlinear optical properties, and analyzed the sources\nof differentiation using the occupied and unoccupied multiband structure\ntheory. The results correspond well to the phenomena observed in the\nultrafast laser, which will provide strong support for the design\nof higher performance photoelectric devices based on topological insulators.