Microscopic molecular optics theory of surface second harmonic generation and sum-frequency generation spectroscopy based on the discrete dipole lattice model

Abstract

Two crucial issues in the interface studies with the interface specific nonlinear spectroscopy are on how to describe the macroscopic dielectric constant of the molecularly thin layer and how to calculate the anisotropic two dimensional microscopic local field effect. In the currently accepted models of the nonlinear optics, the nonlinear radiation was treated as the result of an infinitesimally thin polarization sheet layer, and a three layer model was generally employed. The direct consequence of this approach is that an apriori dielectric constant, which still does not have a clear definition, has to be assigned to this polarization layer. Because the Second Harmonic Generation (SHG) and the Sum-Frequency Generation vibrational Spectroscopy (SFG-VS) have been proven as the sensitive probes for interfaces with the submonolayer coverage, the treatment based on the more realistic discrete induced dipole model needs to be developed. Here we show that following the molecular optics theory approach the SHG, as well as the SFG-VS, radiation from the monolayer or submonolayer at an interface can be rigorously treated as the radiation from an induced dipole lattice at the interface. In this approach, the introduction of the polarization sheet is no longer necessary. Therefore, the ambiguity of the unaccounted dielectric constant of the polarization layer is no longer an issue. Moreover, the anisotropic two dimensional microscopic local field factors can be explicitly expressed with the linear polarizability tensors of the interfacial molecules. Based on the planewise dipole sum rule in the molecular monolayer, crucial experimental tests of this microscopic treatment with SHG and SFG-VS are discussed. Many puzzles in the literature of surface SHG and SFG spectroscopy studies can also be understood or resolved in this framework. This new treatment may provide a solid basis for the quantitative analysis in the surface SHG and SFG studies.

Modeling multilayer thin film interference effects in interface-specific coherent nonlinear optical spectroscopies

“…Input local fields are determined from the internal transfer coefficients and the usual boundary conditions. We envision that this model will have implications in a wide range of problems as straightforward as rational experimental design to some of the more vexing challenges in surface specific spectroscopy, such as quantification of bulk contributions or microscopic local field corrections (i.e., local dipole effects) [30][31][32]. Further, we see this as a step forward for such techniques as nonlinear ellipsometry [33,34] on thin film systems.…”

Sum frequency generation vibrational spectroscopy (SFG-VS) for complex molecular surfaces and interfaces: Spectral lineshape measurement and analysis plus some controversial issues

“…Over the more than three decades since the inception of the surface SFG-VS in the early 1980s [3][4][5], there have been many review articles and a most recent monograph by the founder of the field [6] on the fundamentals theory [7][8][9][10][11][12][13][14][15][16], methods and technical developments [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], specific applications to various systems , and progresses reports [56][57][58][59][60][61][62] of SFG-VS on the studies of the structure and dynamics of various surfaces and interfaces. Instead of repeating what has been covered in the literature, this review aims to focus on the recent progresses and understandings that need to be summarized for the reference of the researchers and students, who are interested in the nonlinear vibrational spectroscopy of complex molecular surfaces and interfaces, by focusing on the new developments on the accurate measurement and analysis of SFG-VS spectral lineshape that is crucial for the applications to complex molecular surfaces and interfaces.…”

IR Absorption, Raman Scattering, and IR-Vis Sum-Frequency Generation Spectroscopy as Quantitative Probes of Surface Structure

“…Definitions and discussion of the local field corrections L and unit polarization vectorsê appear in the literature (71,74,75). Although it is possible to determine the molecular orientation directly from the s-and p-polarized spectra by considering Eqs.…”