Effect of Distribution Pattern of Molecular Dipoles onMicroscopic Second-Harmonic Generation

Abstract

We set up a model for dealing with the second-harmonic generation (SHG)from molecular dipoles in a line alignment pattern rather than a planardistribution under a microscope. Because of this model, it is possibleto perform a flexibly quantitative investigation of SHG from collagenfibres at a molecular level. The line alignment pattern induces moresignificant modifications in both the angular dipole distributionstructure A(θ,φ) and the second-harmonic power structureΘy(θ,φ), compared to a planar distribution. Also, the linealignment angle t has strong effect on A(θ,φ) andΘy(θ,φ), resulting in an irregular SHG angular powerdistribution. That is to say, it is unnecessary for SHG emission topresent two well-defined off-axis lobes. The total SHG power shows twosymmetrical peaks at angles of t = 50° and t = 130° while a drop at t = 90°. The weakest SHGsignals can be measured at t = 0° and t = 180°.