Abstract

Second harmonic generation (SHG) is well known for giving unique information about the properties of crystals,¹ thin films, surfaces, and interfaces of centrosymmetric and non-centrosymmetric materials.² However, for isotropic materials possessing inversion symmetry (such as solutions or suspensions of the molecules of biological importance, for instance), the SHG in the bulk is forbidden in the electro-dipole approximation.^1,2 This effect in the bulk arises only when quadrupole and/or magneto-dipole nonlinear susceptibilities are taken into account. Isotropic nonracemic solutions of mirror-asymmetric (chiral) molecules lack the inversion center, and nonlinear dipole susceptibilities of even orders, which are responsible for SHG nonlinear process, become nonvanishing.³

© 1997 Optical Society of America