IMAGE-CONTRAST IN NEAR-FIELD OPTICS

The resolution of optical microscopy can be extended beyond the diffraction limit by placing a source or detector of visible light having dimensions much smaller than the wavelength, lambda, in the near-field of the sample (< lambda/10). This technique, near-field scanning optical microscopy, is sensitive to a variety of important sample properties including optical density, refractive index, luminescence, and birefringence. Although image contrast based on certain sample characteristics is similar to that observed in traditional optical microscopy, strong coupling between the probe and sample often produces contrast unique to the near-field.