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We present an experimental investigation on third-order nonlinear optical properties of RF-sputtered WSe 2 thin films using a single-beam Z -scan technique around the optical communication window in a near-infrared spectral band. The nonlinear absorption coefficient was obtained from the open-aperture Z -scan transmission using ultrashort pulses centered at 1520 nm excitation wavelength. The results show a reverse saturable absorption signature for all the WSe 2 films due to two-photon absorption (TPA) mediated electronic transitions. The dependency of the TPA coefficient on film thickness is analyzed through the modification in an electronic band structure essentially caused due to defects induced in the samples. In addition, we also explored the impact of high laser intensity on the TPA process, which essentially pointed toward a significant contribution of free-carrier absorption at small laser intensities in WSe 2 thin films. This investigation provides a basis for optimally tailoring the nonlinear optical properties of transition-metal-dichalcogenides via bandgap engineering for improving photonic device functionality. [ABSTRACT FROM AUTHOR]

We present a detailed investigation on the intensity dependent third-order nonlinear optical (NLO) properties of RFsputtered WSe2 thin film using ultra short pulses. The investigation employed a single-beam Z-scan technique using nearinfrared (NIR) ultra short pulses centered at 1030 nm for ascertaining the NLO response. The results reveal a reverse saturable absorption (RSA) signature, which is primarily due to the contribution from two-photon absorption (TPA). We explored the impact of high optical fluence on the TPA process and observed the weakening of the nonlinear optical absorption in WSe2 thin film, which essentially pointed towards a significant contribution of free-carriers as well as bandfilling effect. This research elucidates the insight of photophysical properties of WSe2 thin films and shows the potential use as optical limiters. [ABSTRACT FROM AUTHOR]

We present a comprehensive study on the impact of phase transformations of metallophthalocyanine thin films on their third-order nonlinear optical (NLO) properties. The metallophthalocyanine thin films are prepared by thermally evaporating the commercially available Copper(II)2,9,16,23-Tetra-tert-butyl-29H, 31H-phthalocyanine (CuPc) and Zinc(II) 2,9,16,23-Tetra-tert-butyl-29H, 31Hphthalocyanine (ZnPc) powder on glass substrate. Thermal annealing causes a phase transformation which has a distinct signature in powder X-ray diffraction and UV-Vis-NIR spectroscopy. The NLO characteristics which include nonlinear refractive index n2, as well as nonlinear absorption coefficient (βeff), were measured by using a single beam Z-scan technique. An ultrashort pulsed fiber laser emitting femtosecond pulses (▵ ι≈250 fs) at 1064nm central wavelength is used as a source for the Z-scan experiment. The βeff values in as prepared thin films were ascertained to be smaller as compared to the annealed one due to the smaller value of saturation intensity (Is) which, in turn, is a consequence of ground-state bleaching in the thermally unstable amorphous state of the molecule. Interestingly, the nonlinear refractive indices bear opposite sign for CuPc and ZnPc. The variations in the third-order nonlinearity in CuPc and ZnPc are discussed in terms of molecular packing and geometries of metallophthalocyanine molecules. [ABSTRACT FROM AUTHOR]

We present a detailed investigation on the impact of thermal annealing on the third-order nonlinear optical (NLO) properties of sputtered W S e 2 thin films. The process of annealing results in an appreciable change in morphology and texture of W S e 2 films that is governed by the annealing temperature and duration of annealing. These modifications are apparent from the electron micrographs as well as X-ray diffraction and Raman spectrum. The visible absorption spectroscopy point towards a gradual shrinkage of electronic bandgap which motivated us to explore the impact of NLO properties of the annealed W S e 2 films. The NLO measurements were carried out using a single-beam Z-scan technique using ultrashort pulses centered at 1030 nm excitation wavelength. The investigations reveal a distinct two-photon absorption (TPA) signature for the annealed W S e 2 films along with a self-focusing effect. The observations indicate the strengthening of optical limiting behavior exhibited by W S e 2 films when they are annealed for a longer duration. The outcomes suggest that the process of annealing in W S e 2 films allows controlling the NLO properties and renders them more suitable candidates as optical limiters for high-power applications. • We study a layered transition metal dichalcogenide (TMD), known as WSe 2 and explore the impact of annealing on its nonlinear optical properties. • The process of annealing the WSe 2 thin film results in removal of defects that gets reflected in the electronic bandgap. • This is accompanied by lowering of stress associated with the annealed thin films. • We experimentally show that the improvement in stoichiometry of WSe 2 films leads to a discernible strengthening of nonlinear optical response. • The annealed films shows improved optical limiting characteristics at ultrashort time scales in the infrared spectral band. [ABSTRACT FROM AUTHOR]

We present a detailed investigation on thickness-dependent third-order (χ (3)) nonlinear optical properties of RF-sputtered WSe 2 thin-films using ultrashort pulses centered at different excitation wavelengths. The single-beam Z-scan based investigation in the visible spectrum reveals a predominant Pauli-blocking effect led saturable absorption or optical limiting in WSe 2 thin-films. The study also explores the dispersion in third-order nonlinear susceptibility (χ (3)) in WSe 2 thin films. Interestingly, WSe 2 thin-films of any thickness exhibit a self-focusing effect depicting a positive nonlinear refractive index (n 2 > 0). The frequency-dependent nonlinear absorption (β) bear distinct correlations with the bandgap of the films which is also investigated through density-functional-theory (DFT) based simulations. The alteration in bandstructure is primarily due to the Se -deficiency induced defect bands in WSe 2 thin-films which has discernible impact on the optical limiting characteristics. • The third-order nonlinear optical properties of RF sputtered WSe 2 thin films are investigated. • The thin films exhibit strong Pauli-blocking induced saturable absorption effect which is strongy affected by the defect states/bands emanating from Se-deficiency in the films. • The density-functional-theory (DFT) simulations predict the defect state(s) which closely match with the experimental observations. [ABSTRACT FROM AUTHOR]