RESUMEN
Carotenoids are a class of natural pigments that play a fundamental role in photosynthesis and optoelectronics. However, the complexity of their energy level structure and electronic states has prevented a clear interpretation of their photophysics and photochemistry. The mediating nonradiative decay of the bright S2 state to the dark S1 state of carotenoids involves a population of bridging intermediate state. Herein, time-dependent DFT was used to study the energy level and electronic excitation process of ß-carotene. A π-π* transition and π electron delocalization of electron excitation could be inferred based on the difference in the electron cloud distribution of the HOMO and LUMO orbitals. Through the electronic transition contribution in the UV-vis spectra and the electron density difference between the ground state and the excited state, the electronic energy level structure and possible dark state were analyzed. On this basis, the electronic excitation process of ß-carotene was theoretically studied by combining electron-hole analysis and transition density matrix (TDM). There was a charge transfer from the ß-ionone ring to the long-chain in the (S0) â (S2), (S0) â (S4) and (S0) â (S5).
RESUMEN
The cascaded stimulated Raman scattering (SRS) of an aqueous sodium sulfate solution was investigated as well as the generation of the crossing-pump effect. With the introduction of dual sample cells, the first-order Stokes of the O-H stretching vibrational mode was able to act as the pump light to excite the Stokes of the S-O stretching vibrational mode, and a new Raman peak was obtained at 4423 cm-1. The dual sample cell device not only lowered the SRS threshold, but also enhanced the four-wave mixing (FWM) process. Compared to the input laser of 7 ns/pulse, the first-order Stokes of O-H was compressed to a pulse width of 413 ps after passing through the dual sample cells. The SRS of aqueous sodium sulfate solution covered an ultrabroad wavelength ranging from 441 nm to 720 nm (a Raman shift ranging from -3859 cm-1 to 4923 cm-1). The cone-shaped launch ring of the FWM process was also recorded. This work provides a reference for the establishment of laser frequency conversion devices using an aqueous sodium sulfate solution as the Raman medium.
RESUMEN
The hydrogen bond (HB) network structure and kinetics of the acetone-water mixed solutions were investigated by the spontaneous Raman and stimulated Raman scattering (SRS) spectra. The HB network of water molecules was enhanced when the volume fraction of acetone ranged from 0 to 0.25. Two new SRS peaks of water at 3272 and 3380 cm-1 were obtained, resulting from the cooperation of the polar carbonyl (C = O)-enhanced HB and the ice-like structure formed around the methyl groups. However, when the volume fraction went beyond 0.25, the spontaneous Raman main peak at 3445 cm-1 showed a significant blue-shift, and the corresponding SRS signal disappeared, indicating that the HB of water was weakened, which originated from the self-association of acetone. In the meantime, the fully tetrahedral HB structure among water molecules was destroyed at the higher volume fraction (≥ 0.8). Hopefully, our study here would advance the study of HB network structures and kinetics in other aqueous solutions.
RESUMEN
Stimulated Raman scattering (SRS) in a liquid has been a major focus of nonlinear optics. Traditional SRS generates single or cascaded Stokes components arising from spontaneous Raman noise. Herein, we report the formation mechanism of a specific spectrum-continuous spectroscopy technique based on SRS of mixed liquids. SRS of a mixed acetone and carbon disulfide solution is investigated by a pulsed Nd:YAG laser with a wavelength of 532â nm. Two remarkably asymmetric broadened SRS lines are obtained. When the volume ratio is 7:3, the broadened spectral bands are optimized. The supercontinuum spectroscopy phenomenon is explained by hydrogen bond formation, adjacent vibrational modes coupling, and laser-induced plasma generation. This technique has the potential to contribute to the development of a supercontinuum Raman laser.
