title: Broadband ultrafast nonlinear absorption and nonlinear refraction of layered molybdenum dichalcogenide semiconductors.
abstract: A series of layered molybdenum dichalcogenides, i.e., MoX₂ (X = S, Se and Te), were prepared in cyclohexyl pyrrolidinone by a liquid-phase exfoliation technique. The high quality of the two-dimensional nanostructures was verified by transmission electron microscopy and absorption spectroscopy. Open- and closed-aperture Z-scans were employed to study the nonlinear absorption and nonlinear refraction of the MoX₂ dispersions, respectively. All the three-layered nanostructures exhibit prominent ultrafast saturable absorption (SA) for both femtosecond (fs) and picosecond (ps) laser pulses over a broad wavelength range from the visible to the near infrared. While the dispersions treated with low-speed centrifugation (1500 rpm) have an SA response, and the MoS₂ and MoSe₂ dispersions after higher speed centrifugation (10,000 rpm) possess two-photon absorption for fs pulses at 1030 nm, which is due to the significant reduction of the average thickness of the nanosheets; hence, the broadening of band gap. In addition, all dispersions show obvious nonlinear self-defocusing for ps pulses at both 1064 nm and 532 nm, resulting from the thermally-induced nonlinear refractive index. The versatile ultrafast nonlinear properties imply a huge potential of the layered MoX2 semiconductors in the development of nanophotonic devices, such as mode-lockers, optical limiters, optical switches, etc.
authors.affiliation: Key Laboratory of Materials for High-Power Laser, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai 201800, China.
authors.forename: Kangpeng
authors.initials: K
authors.lastname: Wang
authors.forename: Yanyan
authors.initials: Y
authors.lastname: Feng
authors.forename: Chunxia
authors.initials: C
authors.lastname: Chang
authors.forename: Jingxin
authors.initials: J
authors.lastname: Zhan
authors.forename: Chengwei
authors.initials: C
authors.lastname: Wang
authors.forename: Quanzhong
authors.initials: Q
authors.lastname: Zhao
authors.forename: Jonathan N
authors.initials: JN
authors.lastname: Coleman
authors.forename: Long
authors.initials: L
authors.lastname: Zhang
authors.forename: Werner J
authors.initials: WJ
authors.lastname: Blau
authors.forename: Jun
authors.initials: J
authors.lastname: Wang