Direct Observation of Degenerate Two-Photon Absorption and Its Saturation in WS2 and MoS2 Monolayer and Few-Layer Films

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• 作者：Saifeng Zhang ; Ningning Dong ; Niall McEvoy ; Maria O鈥橞rien ; Sin茅ad Winters ; Nina C. Berner ; Chanyoung Yim ; Yuanxin Li ; Xiaoyan Zhang ; Zhanghai Chen ; Long Zhang ; Georg S. Duesberg ; Jun Wang
• 刊名：ACS Nano
• 出版年：2015
• 出版时间：July 28, 2015
• 年：2015
• 卷：9
• 期：7
• 页码：7142-7150
• ISSN：1936-086X

文摘

The optical nonlinearity of WS₂ and MoS₂ monolayer and few-layer films was investigated using the Z-scan technique with femtosecond pulses from the visible to the near-infrared range. The nonlinear absorption of few- and multilayer WS₂ and MoS₂ films and their dependences on excitation wavelength were studied. WS₂ films with 1鈥? layers exhibited a giant two-photon absorption (TPA) coefficient as high as (1.0 卤 0.8) 脳 10⁴ cm/GW. TPA saturation was observed for the WS₂ film with 1鈥? layers and for the MoS₂ film with 25鈥?7 layers. The giant nonlinearity of WS₂ and MoS₂ films is attributed to a two-dimensional confinement, a giant exciton effect, and the band edge resonance of TPA.