Nonlinear coherent four-wave mixing in optical microscopy

An analysis of the imaging properties of nonlinear coherent four-wave mixin g optical microscopes is presented. The generation and propagation of coher ent signals are considered under conditions of high numerical aperture with a model that circumvents the need to use the slowly varying envelope appro ximation. Calculations of coherent anti-Stokes Raman scattering signals sho w that diffraction effects play a prominent role in the spatial distributio n of the coherent signal intensity. It is emphasized that, unlike for fluor escence microscopy, the detected signal is not a straightforward convolutio n of a point-spread function and the object but is shaped by the complex in terplay of object size and coherent buildup dynamics. (C) 2000 Optical Soci ety of America.