Theory of second-harmonic generation from a sphere of centrosymmetric material

Summary form only given. Optical second-harmonic generation (SHG) has been widely demonstrated as a surface-specific probe of centrosymmetric media. Applications of the method and the corresponding theoretical formulations have been limited primarily to planar surfaces and interfaces. Recently, however, experimental studies have demonstrated the sensitivity of SHG to the surface of spherical particles of dimensions as small as /spl sim/100 nm. These results offer the promise of an extension of the SHG technique to a new class of systems of physical and chemical interest. The sensitivity of SHG to surfaces arises from the fact that in the dipole approximation, SHG is forbidden in a medium that possesses inversion symmetry. The inversion symmetry is broken at the interface, thus making SHG allowed. This same property, however, introduces difficulties in understanding SHG from the surface of a small spherical particle: in the electric-dipole limit, the overall symmetry of a spherical object implies that the SHG process is forbidden. Hence our goal is to develop a theory beyond the dipole approximation to describe the observed SHG process.