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Ultra-broadband Nonlinear Saturable Absorption for Two-dimensional Bi 2 Te x Se 3 − x Nanosheets

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ABSTRACT

We report the ultra-broadband nonlinear optical (NLO) response of Bi2TexSe3−x nanosheets produced by a facile solvothermal method. Our result show that the extracted basic optical nonlinearity parameters of Bi2TexSe3−x nanosheets, αNL, Imχ(3), and FOM reach ~104 cm/GW, ~10−8 esu and ~10−13 esu cm, respectively, which are several orders of magnitude larger than those of bulk dielectrics. We further observed the excitation intensity dependence of the NLO absorption coefficient and the NLO response sensitivity. The mechanisms of those phenomena were proposed based on physical model. The wavelength dependence of the NLO response of Bi2TexSe3−x nanosheets was investigated, and we determined that the Bi2TexSe3−x nanosheets possess an ultra-broadband nonlinear saturable absorption property covering a range from the visible to the near-infrared band, with the NLO absorption insensitive to the excitation wavelength. This work provide fundamental and systematic insight into the NLO response of Bi2TexSe3−x nanosheets and support their application in photonic devices in the future.

No MeSH data available.


Schematic diagram of optical saturable absorption in Bi2TexSe3−x nanosheets.CB: Conduction band; VB: Valence band.
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f4: Schematic diagram of optical saturable absorption in Bi2TexSe3−x nanosheets.CB: Conduction band; VB: Valence band.

Mentions: Figure 3(a–d) show the Z-scan traces of the Bi2TexSe3−x nanosheets that were obtained by a 532-nm laser pulse at different excitation intensities. All of the curves exhibit a “bell shape”, which is induced by the saturable absorption effect (negative NLO absorption). Bi2TexSe3−x nanosheets normally have a narrow band gap (0.15 ~ 0.3 eV)36, so it is reasonable to assume that the one-photon induced absorption dominates the NLO process with a photon energy of 0.8 ~ 2.33 eV (λ = 532 nm ~ 1550 nm). The saturable absorption mechanism can be explained as follows: under weak excited light with a photon energy larger than the bulk state bandgap, the electrons in the valence band can be excited to the conduction band and then occupy states in the conduction band, whereas under a high enough intensity of excited light, all the available states in the conduction band are occupied by photo-generated carriers; owing to the Pauli blocking principle, an optical bleaching effect occurs (i.e., saturable absorption). A schematic diagram is shown in Fig. 4.


Ultra-broadband Nonlinear Saturable Absorption for Two-dimensional Bi 2 Te x Se 3 − x Nanosheets
Schematic diagram of optical saturable absorption in Bi2TexSe3−x nanosheets.CB: Conduction band; VB: Valence band.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5016803&req=5

f4: Schematic diagram of optical saturable absorption in Bi2TexSe3−x nanosheets.CB: Conduction band; VB: Valence band.
Mentions: Figure 3(a–d) show the Z-scan traces of the Bi2TexSe3−x nanosheets that were obtained by a 532-nm laser pulse at different excitation intensities. All of the curves exhibit a “bell shape”, which is induced by the saturable absorption effect (negative NLO absorption). Bi2TexSe3−x nanosheets normally have a narrow band gap (0.15 ~ 0.3 eV)36, so it is reasonable to assume that the one-photon induced absorption dominates the NLO process with a photon energy of 0.8 ~ 2.33 eV (λ = 532 nm ~ 1550 nm). The saturable absorption mechanism can be explained as follows: under weak excited light with a photon energy larger than the bulk state bandgap, the electrons in the valence band can be excited to the conduction band and then occupy states in the conduction band, whereas under a high enough intensity of excited light, all the available states in the conduction band are occupied by photo-generated carriers; owing to the Pauli blocking principle, an optical bleaching effect occurs (i.e., saturable absorption). A schematic diagram is shown in Fig. 4.

View Article: PubMed Central - PubMed

ABSTRACT

We report the ultra-broadband nonlinear optical (NLO) response of Bi2TexSe3−x nanosheets produced by a facile solvothermal method. Our result show that the extracted basic optical nonlinearity parameters of Bi2TexSe3−x nanosheets, αNL, Imχ(3), and FOM reach ~104 cm/GW, ~10−8 esu and ~10−13 esu cm, respectively, which are several orders of magnitude larger than those of bulk dielectrics. We further observed the excitation intensity dependence of the NLO absorption coefficient and the NLO response sensitivity. The mechanisms of those phenomena were proposed based on physical model. The wavelength dependence of the NLO response of Bi2TexSe3−x nanosheets was investigated, and we determined that the Bi2TexSe3−x nanosheets possess an ultra-broadband nonlinear saturable absorption property covering a range from the visible to the near-infrared band, with the NLO absorption insensitive to the excitation wavelength. This work provide fundamental and systematic insight into the NLO response of Bi2TexSe3−x nanosheets and support their application in photonic devices in the future.

No MeSH data available.