Second-harmonic generation by focused excitation of inhomogeneously distributed scatterers

We generalize a simple model describing second-harmonic generation (2HG) by highly focused excitation light to allow the possibility of sample inhomogeneities. Depending on their spatial frequencies these inhomogeneities can significantly modify the 2HG radiation patterns and total powers, and in certain cases provoke backward 2HG propagation. Examples are considered where the distribution of 2HG radiators is axially periodic or spherically localized, illustrating the effects of sample structure or clustering. Our model is specifically applicable to 2HG microscopy geometries. (C) 2001 Published by Elsevier Science B.V.