Optically Controlled Extraordinary Terahertz Transmission of Bi2Se3 Film Modulator
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Standing on the potential for high-speed modulation and switching in the terahertz (THz) regime, all-optical approaches whose response speeds mainly depend on the lifetime of nonequilibrium free carriers have attracted a tremendous attention. Here, we establish a novel bi-direction THz modulation experiment controlled by femtosecond laser for new functional devices. Specifically, time-resolved transmission measurements are conducted on a series of thin layers Bi2Se3 films fabricated straightforwardly on Al2O3 substrates, with the pump fluence range from 25 μJ/cm2 to 200 μJ/cm2 per pulse. After photoexcitation, an ultrafast switching of THz wave with a full recovery time of ~10 ps is observed. For a longer timescale, a photoinduced increase in the transmitted THz amplitude is found in the 8 and 10 quintuple layers (QL) Bi2Se3, which shows a thickness-dependent topological phase transition. Additionally, the broadband modulation effect of the 8 QL Bi2Se3 film is presented at the time delays of 2.2 ps and 12.5 ps which have a maximum modulation depth of 6.4% and 1.3% under the pump fluence of 200 μJ/cm2, respectively. Furthermore, the absorption of α optical phonon at 1.9 THz shows a time-dependent evolution which is consistent with the cooling of lattice temperature.
KeywordsUltrafast optics topological insulator ultrafast photonic devices
This work was partially supported by Opening Foundation of State Key Laboratory of High Performance Computing (Grant Nos. 201601–01, 201601–02, and 201601-03); Scientific Researches Foundation of National University of Defense Technology (Grant No. zk16-03-59); Open Research Fund of Hunan Provincial Key Laboratory of High Energy Technology (Grant No. GNJGJS03); Director Fund of State Key Laboratory of Pulsed Power Laser Technology (Grant No. SKL2018ZR05); Opening Foundation of State Key Laboratory of laser and matter interaction (Grant No. SKLLIM1702).
The Opening Foundation of State Key Laboratory of High Performance Computing (Grant Nos. 201601-01, 201601-02, and 201601-03) plays the role of designing the subject and materials growth. The Director Fund of State Key Laboratory of Pulsed Power Laser Technology (Grant No. SKL2018ZR05) and the Opening Foundation of State Key Laboratory of laser and matter interaction (Grant No. SKLLIM1702) play the role of data collection and analysis. The Scientific Researches Foundation of National University of Defense Technology (Grant No. zk16-03-59) and the Open Research Fund of Hunan Provincial Key Laboratory of High Energy Technology (GNJGJS03) play the role of data interpretation and manuscript writing.
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