Theoretical Framework for SHG Microscopy: A Matrix-Based Approach
Before tackling nonlinear optical eects, it arguably makes sense to describe linear optical eects within the same conceptual framework to better understand the close similarities. At the single molecule level, the linear polarizability describes the magnitude and phase of the dipole induced in the molecule by an AC or DC eld. For an isolated molecule at optical frequencies, the linear polarizability describes optical scattering. When the density of scattering centers is high enough such that many are located distances much less than the optical wavelength, interference between the collective set of individual dipoles leads to directional reection and refraction of light.