Modeling Coherent Anti-Stokes Raman Scattering with Time-Dependent Density Functional Theory: Vacuum and Surface Enhancement.

Abstract

We present the first density functional simulations of coherent anti-Stokes Raman scattering (CARS) and an analysis of the chemical effects upon binding to a metal surface. Spectra are obtained from first-principles electronic structure calculations and are compared with available experiments and previously available theoretical results following from Hartree–Fock polarizability derivatives. A first approximation to the nonresonant portion of the CARS signal is also explored. We examine the silver pyridine cluster models of the surface chemical signal enhancement, previously introduced for surface-enhanced Raman scattering. Chemical resonant intensity enhancements of roughly 102 are found for several model clusters. The prospects of realizing further enhancement of CARS signal with metal surfaces is discussed in light of the predicted chemical enhancements.

Coupled wave equations theory of surface-enhanced femtosecond stimulated Raman scattering

“…While the dispersive nature of the lineshapes was originally hypothesized to be purely Fano-like interferences, 15 our analysis suggests that they are a combination of two Fano-like contributions. Similar to previously observed dispersive lineshapes that originate from multiple physical interference processes, 21,22 the lineshapes in this work are attributed to interference of the real and imaginary components of the Raman susceptibility with the LFE of the Stokes field interacting with a plasmonic particle.…”

“…20 Research into the lineshapes observed in surfaceenhanced coherent Raman scattering has focused primarily on SECARS. 21,22 In SECARS, dispersive lineshapes in the vibrational spectrum are observed due to interference of the vibrationally resonant signal with electronically resonant four-wave mixing signals, similar to the lineshapes seen in CARS. One paper has investigated the plasmonicenhancement in SE-SRS; however, the theory only considered single vibrational modes and resulted in Lorentzian lineshapes.…”

“…4. Probing both the real and imaginary portions of χ R (ω) will lead to interference and dispersive lineshapes as seen in SECARS (but with a different mechanism) 21,22 and previous SE-FSRS experiments. 14,15 To fully understand the Raman gain optical density, we re-evaluate Eqs.…”

Time-Resolved Surface-Enhanced Coherent Sensing of Nanoscale Molecular Complexes

“…Time-resolved tip-enhanced CARS spectroscopy7 and subwavelength microscopy could be realized by extension of the present approach. Spectral interpretation could be facilitated by using higher levels of theory and by direct modeling of the surface-enhanced CARS signals28. With further developments tr-SECARS could achieve ultrashort sub-picosecond signal acquisition and single shot real-time detection capabilities.…”

Measurement of the third‐order nonlinear optical susceptibility χ(3) for the 1002‐cm–1 mode of benzenethiol using coherent anti‐Stokes Raman scattering with continuous‐wave diode lasers

“…Microscopic CARS susceptibilities have been simulated for this work using time‐dependent density functional theory, employing the PBE0 functional and def2‐TZVP basis within a locally modified version of the TURBOMOLE program package. At the level of theory employed, the CARS susceptibility is modeled as a product of polarizability derivatives along harmonic nuclear modes.…”