Exceptional ultrafast nonlinear optical response of functionalized silicon nanosheets

Aqueous Dispersion of Xenes by Liquid Phase Exfoliation of Monoelemental Crystals in Melamine Solution

Αfter the impressive evolution of graphene and its derivatives, a large number of two dimensional (2D) materials with important optical and electrical properties have been successfully fabricated. Liquid phase exfoliation (LPE) of layered and non-layered materials has become a widely applied method for the preparation of 2D nanostructures with an extensive variety of applications. However, in most cases organic solvents are used as liquid phase which are often toxic and environmentally unfriendly and lead to low yields. In this work, we present water as a suitable liquid phase and dispersion medium for the exfoliation of layered and non-layered monoelemental solids from IVA, VA and VIA groups of the periodic table, such as silicon, tin, bismuth and tellurium. The 2D nanostructures, silicene, stanene, bismuthene and tellurene are therefore prepared by a completely sustainable and environmentally friendly method. The prepared Xenes, as they are called, are fully characterized by microscopic and spectroscopic techniques.

Excitonic Effects on the Ultrafast Nonlinear Optical Response of MoS2 and Fluorinated Graphene/MoS2 Heterostructure Films for Photonic Applications

In the present work, the ultrafast nonlinear optical (NLO) response of some molybdenum disulfide (MoS2), fluorinated graphene (FG), and FG/MoS2 heterostructure thin films was studied using the Z-scan and optical Kerr effect techniques employing femtosecond laser pulses at different excitation wavelengths (i.e., 400, 570, 610, 660, 800, and 1200 nm). The experiments have shown that the NLO response of the MoS2 and MoS2/FG films was significantly enhanced when the films were excited with 400, 610, and 660 nm laser pulses due to resonance effects with the close-lying excitons in these nanostructures. For a better evaluation of the resonant enhancement of the NLO response, measurements were also carried out at off-resonant wavelengths, i.e., at 570, 800, and 1200 nm. The presence of excitons in the MoS2 and MoS2/FG films resulted in strong saturable absorption and self-defocusing, with exceptionally large values of third-order susceptibilities χ(3) ranging from 10-12 to 10-13 esu. In addition, the NLO response of the MoS2/FG heterostructure was found to be stronger than that of the individual MoS2 and FG films, most probably attributed to interlayer carrier transfer. The determined NLO parameters of the studied nanostructures were found to be comparable to, and in some cases exceeded, those of other reported 2D materials known to exhibit a strong NLO response as well. These findings not only advance the fundamental understanding of the contributions of excitons on the NLO response/properties of transition metal dichalcogenide-based ultrathin films but also highlight the importance of excitons for tailoring their NLO response in view of various applications in advanced optoelectronics and photonic devices.

Push-Pull Carbazole-Based Dyes: Synthesis, Strong Ultrafast Nonlinear Optical Response, and Effective Photoinitiation for Multiphoton Lithography

The present work reports on the ultrafast nonlinear optical (NLO) properties of a series of D-π-Α and D-A push-pull carbazole-based dyes and establishes a correlation between these properties and their efficiency for potential photonic and optoelectronic applications such as multiphoton lithography (MPL). The ultrafast NLO properties of the studied dyes are determined by two distinct experimental techniques, Z-scan and pump-probe optical Kerr effect (OKE), employing 246 fs laser pulses at 515 nm. The results indicate that chemical functionalization of the carbazole moiety with various strong electron-donating and/or electron-withdrawing groups, such as benzene, styrene, 4-bromostyrene, nitrobenzene, trimethyl isocyanurate, methyl, and indane-1,3-dione, can result in a controlled and significant enhancement of the NLO absorptive and refractive responses. In the context of potential applications, the efficiency of carbazole-based organic materials as photoinitiators (PIs) for MPL applications is demonstrated. The fabricated woodpile microstructure using chemically functionalized carbazole as a PI demonstrates improvements in both feature size and MPL efficiency compared to that using unfunctionalized carbazole as a PI. This is attributed to the efficient charge transfer resulting from chemical functionalization, which leads to a substantial increase (approximately 1 order of magnitude) in the values of the imaginary part of the second-order hyperpolarizability (Imγ) and the two-photon absorption cross section (σ). The achieved feature size of 280 nm is comparable to that obtained with other widely used PIs in MPL applications. Additionally, owing to the strong NLO properties of the studied functionalized carbazole, they could also be promising candidates for further applications in photonics and optoelectronics.

A 1064 nm laser adaptive limiter with visible light transparency based on one dimensional photonic crystals of LiNbO3 defects

Herein, we present the investigation of the visible light transparency and optical limiting characteristics of one dimensional photonic crystals with LiNbO3 defects fabricated by the sputtering technique. Transmission spectroscopy measurements reveal a broad photonic band gap with a 1064 nm defect mode and high transmittance within the visible range. The optical energy limiting performance in the photonic crystal can be attributed to the strong confinement of the optical field surrounding the LiNbO3 defect layer. The low energy 1064 nm laser demonstrates a transmittance of 82.15%. Notably, the optical limiting threshold is lower at 62.03 mJ cm-2 in comparison with conventional optical limiting materials. Additionally, the optical limiter achieves a transmittance of 68.57% within the visible light band.