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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 report here a set of triaryl pyrazole based B−N coordinated boron compounds (11‐17) synthesized by electrophilic aromatic borylation strategy. All the pyrazole boron compounds were thoroughly characterized using multinuclear NMR spectroscopy, LC–MS, and single crystal X‐ray diffraction analysis (for 12–17). The photoluminescence measurements of 11–17 revealed that the emission peak maxima were tuned based on the substitution on N‐phenyl. The photophysical and electrochemical properties were further supported by theoretical calculations. Z‐scan based investigations at 515 nm pump wavelength showed that B−N coordination led to enhancement of nonlinear absorption (two‐photon absorption (TPA)) in these compounds if an electron deficient moiety is attached. It has also been observed that an appropriate choice of moiety allows to optimally maneuver the molecular polarizability of the π‐system and consequently, assists in controlling the third‐order nonlinear optical response. [ABSTRACT FROM AUTHOR]

Intramolecular B ← N coordinated fluorophores have shown potential applications in optoelectronics and as sensors due to their unique photophysical properties. In this work, we report the synthesis and characterization of π-conjugated boron doped phenanthroimidazole dimers. All the π-conjugated B ← N coordinated phenanthroimidazole dimers exhibited high quantum yields in solution (up to 99%) and moderate quantum yields in the solid state (up to 51%). We investigated the nonlinear optical properties of phenanthroimidazole dimers and found that the measurement of two-photon-absorption cross-section is correlated with the conjugation length. [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]