A real-time time-dependent density functional theory method coupled with the classical electrodynamics finite difference time domain technique is employed to systematically investigate the optical properties of hybrid systems composed of silver nanoparticles (NPs) and organic adsorbates.

The feature of the Fano resonance and the influence of quantum interferences on the absorption lineshapes have been revealed.

Vibrational spectroscopy is a powerful tool for probing molecular structures and dynamics since it offers a unique fingerprint that allows molecular identification. One of important aspects of applying vibrational spectroscopy is to develop the probes that can characterize the related properties of molecules such as the conformation and intermolecular interaction. Many examples of vibrational probes have appeared in the literature, including the azide group (–N₃), amide group (–CONH₂), nitrile groups (–CN), hydroxyl group (–OH), –CH group and so on. Among these probes, the –CH group is an excellent one since it is ubiquitous in organic and biological molecules and the C–H stretching vibrational spectrum is extraordinarily sensitive to the local molecular environment. However, one challenge encountered in the application of C–H probes arises from the difficulty in the accurate assignment due to spectral congestion in the C–H stretching region. In this paper, recent advances in the complete assignment of C–H stretching spectra of aliphatic alcohols and the utility of C–H vibration as a probe of the conformation and weak intermolecular interaction are outlined. These results fully demonstrated the potential of the –CH chemical group as a molecular probe.

The nonlinear optical properties of hybrid systems composed of a silver nanosphere and an open-ended finite-sized armchair single-walled carbon nanotube (SWCNT) are systematically investigated by the hybrid time-dependent Hartree–Fock (TDHF)/finite difference time domain (FDTD) approach, which combines the real-time TDHF approach for the molecular electronic dynamics with the classical computational electrodynamics approach, the FDTD, for solving Maxwell’s equations. The high order harmonic generation (HHG) spectra of SWCNTs are studied as a function of the intensity (I₀) and frequency (ω₀) of the incident field, and SWCNTs length as well. It is found that the near field generated by a Ag nanoparticle has an overall enhancement to the molecular HHG in all the energy range, and it extends the HHG spectra to high energy. The inhomogeneity of the near field results in the appearance of even-order harmonics, and their corresponding spectral intensities are sensitive to ω₀, therefore the near field’s gradient. When ω₀ is far away from the frequency of plasmon resonance of the silver nanosphere (ω_c), the interference between the incident and scattering light beams extends the spectral range and makes the HHG spectra more sensitive to I₀, while at ω₀ = ω_c, the impact of the interference on the spectra is negligible.

In this study, the plasmon-enhanced high-order harmonic generation (HHG) of H-terminated finite-sized armchair single-walled carbon nanotubes (SWCNTs) near Ag nanoparticles is investigated systematically. Multiscale methods that combine the real-time time-dependent Hartree–Fock (TDHF) approach at the semi-empirical intermediate neglected differential overlap (INDOS) Hamiltonian level for molecular electronic dynamics with the finite-difference time-domain (FDTD) and solving Maxwell’s equations are used. It is found that for intact CNTs, HHG is significantly enhanced due to plasmon resonance. However, the nonlinear optical properties are saturated when the tube length increases enough in the inhomogeneous near-field. For long CNTs, the large gradient of a near-field is unfavorable for the nonlinear excitation of electrons. But defects can further change the properties of the spectra. The HHG of hybrid systems can be enhanced very clearly by introducing vacancy defects in CNTs. This enhancement is affected by the energy and intensity of the incident light, the near-field gradient, and the number and location of defects.

As one of popular coherent Raman scattering (CRS) techniques, stimulated Raman scattering (SRS) has made significant progress in recent years, especially in label-free biological imaging. Polarization provides an additional degree of freedom to manipulate SRS process. In previous studies, only linearly polarized SRS was fully investigated, in which both pump and Stokes laser fields are linearly polarized. Here we theoretically analyzed SRS process excited by two circularly polarized laser fields and then experimentally demonstrated it by taking spherical symmetric CH₄ molecule as a model system. The experimental results are in good agreement with theoretical ones. It is shown that circularly polarized SRS (CP-SRS) has unique characteristics different from linear polarization. When the handedness of circular polarization states of two laser fields is the same, CP-SRS further suppresses the depolarized vibrational band while keeping the polarized band almost unaffected. On the other hand, when the handedness is opposite, CP-SRS enhances the depolarized band while suppressing the polarized band. Therefore, the CP-SRS not only allows to resolve the symmetry of vibrational modes, but also can enhance vibrational contrast based on symmetry selectivity by suppressing or enhancing the signal from a specific vibrational mode. These results will have potential applications in improving chemical selectivity and imaging contrast as well as spectral resolution SRS microscopy. In addition, the CP-SRS has an ability to determine the depolarization ratio r and identify the overlapping Raman bands.