摘要
Here, we used the micro P-scan method to investigate the saturated absorption(SA) of different layered Bi_2Se_3 continuous films. Through resonance excitation, first, we studied the influence of the second surface state(SS) on SA. The second SS resonance excitation(～2.07 e V) resulted in a free carrier cross section that was 4 orders of magnitude larger than usual. At the same time, we found that the fast relaxation process of the massless Dirac electrons is much shorter than that of electrons in bulk states. Moreover, the second SS excitation resonance reduced the saturation intensity. Second, we studied the effect of the thickness on the SA properties of materials.The results showed that the saturation intensity was positively correlated to the thickness, the same as the modulation depth, and the thicker the Bi_2Se_3 film was, the less the second SS would influence it. This work demonstrated that by using Bi_2Se_3 as a saturable absorber through changing the thickness or excitation wavelength, a controllable SA could be achieved.
Here, we used the micro P-scan method to investigate the saturated absorption （SA） of different layered Bi2Se3 continuous films. Through resonance excitation, first, we studied the influence of the second surface state （SS） on SA. The second SS resonance excitation （-2.07 eV） resulted in a free carrier cross section that was 4 orders of magnitude larger than usual. At the same time, we found that the fast relaxation process of the massless Dirac electrons is much shorter than that of electrons in bulk states. Moreover, the second SS excitation resonance reduced the saturation intensity. Second, we studied the effect of the thickness on the SA properties of materials. The results showed that the saturation intensity was positively correlated to the thickness, the same as the modulation depth, and the thicker the Bi2Se3 film was, the less the second SS would influence it. This work demonstrated that by using BieSe3 as a saturable absorber through changing the thickness or excitation wavelength, a controllable SA could be achieved.
基金
Opening Foundation of State Key Laboratory of High Performance Computing(201601-01,201601-02,201601-03)
Scientific Researches Foundation of National University of Defense Technology(zk16-03-59)
Open Research Fund of State Key Laboratory of Pulsed Power Laser Technology(SKL2017KF06)
Funds for International Cooperation and Exchange of National Natural Science Foundation of China(NSFC)(60921062,61120106)
Director Fund of State Key Laboratory of Pulsed Power Laser Technology(SKL2018ZR05)
