Enhanced stimulated raman scattering of solvent due to anharmonic energy transfer from resonance raman solute molecules.

A new nonlinear optical process, named enhanced stimulated Raman scattering (ESRS), is reported for the first time from resonance Raman in ß-carotene-methanol solution. It is well known that absorption decreases the efficiency of the nonlinear optical and laser processes; however, we observed enhanced stimulated Raman peaks at the first and second Stokes from methanol solvent at 2834 cm-1 with the addition of ß-carotene solutes. This enhanced SRS effect in methanol is attributed to the resonance Raman (RR) process in ß-carotene, which creates a significant number of vibrations from RR and the excess vibrations are transferred to methanol from anharmonic vibrational interactions between the ß-carotene solutes and the methanol solvent, and consequently leads to the increased Raman gain.

Resonance Raman scattering of ß-carotene solution excited by visible laser beams into second singlet state.

This study aimed to use self-absorption correction to determine the Raman enhancement of ß-carotene. The Raman spectra of ß-carotene solutions were measured using 488nm, 514nm, 532nm and 633nm laser beams, which exhibited significant resonance Raman (RR) enhancement when the laser energy approaches the electronic transition energy from S0 to S2 state. The Raman intensity and the actual resonance Raman gain without self-absorption from S2 state by ß-carotene were also obtained to evaluate the effect of self-absorption on RR scattering. Moreover, we observed the Raman intensity strength followed the absorption spectra. Our study found that, although 488nm and 514nm pumps seemed better for stronger RR enhancement, 532nm would be the optimum Raman pump laser with moderate RR enhancement due to reduced fluorescence and self-absorption. The 532nm excitation will be helpful for applying resonance Raman spectroscopy to investigate biological molecules in tissues.

Hybrid generation and analysis of vector vortex beams.

A method is described for generating optical vector vortex beams carrying superpositions of orbital angular momentum states by using a tandem application of a spatial light modulator with a vortex retarder. The vortex component has a spatially inhomogeneous phase front that can carry orbital angular momentum, and the vector nature is a spatially inhomogeneous state of polarization in the laser beam profile. The vector vortex beams are characterized experimentally by imaging the beams at points across the focal plane in an astigmatic system using a tilted lens. Mathematical analysis of the Gouy phase shows good agreement with the phase structure obtained in the experimental images. The polarization structure of the vector beam and the orbital angular momentum of the vortex beam are shown to be preserved.

Oxidized g-C3 N4 Nanospheres as Catalytically Photoactive Linkers in MOF/g-C3 N4 Composite of Hierarchical Pore Structure.

A unique composite of the copper-based metal-organic framework (Cu-benzene tricarboxylic acid (BTC)) with oxidized graphitic carbon nitride nanospheres is synthesized. For comparison, a hybrid material consisting of g-C3 N4 and Cu-BTC is also obtained. Their surface features are analyzed using Fourier transform infrared spectroscopy, X-ray diffraction, sorption of nitrogen, thermal analysis, scanning electron microscopy, photoluminescence, and diffuse reflectance UV-Vis spectroscopy. The results suggest that the formed nanospheres of oxidized g-C3 N4 act as linkers between the copper sites, playing a crucial role in the composite building process. Their incorporation to the Cu-BTC framework causes the development of new mesoporosity. Remarkable alterations in the optical properties, as a result of the coordination of oxygen containing functional groups of the oxidized graphitic carbon nitride to the copper atoms of the framework, suggest an increase in photoreactivity. On the other hand, for the hybrid material consisting of Cu-BTC and g-C3 N4 , the unaltered pore volume and optical properties support the formation of a physical mixture rather than of a composite. The tests on reactive adsorption and detoxification of G-series organophosphate nerve agent surrogate show the enhanced performance of the composite as catalysts and photocatalyst in visible light.