Optical contrast on the surface of mesoscale air–dielectric structures was evaluated with collection-mode near-field scanning optical microscopy. When air holes (300 nm) were smaller than the incident wavelength (400 or 600 nm), the optical field was concentrated in the dielectric region. When air holes (1000 nm) were larger than the incident wavelength (400 or 600 nm), there was topographic edge enhancement. After confirmation with finite-difference time-domain simulation, we conclude that light diffracted off topographic edges is a major contributor to contrast in collection-mode near-field optical images.
© 2003 Optical Society of America
Pei-Kuen Wei, Hsieh-Li Chou, and Wei-Lun Chang, "Diffraction-induced near-field optical images in mesoscale air–dielectric structures," J. Opt. Soc. Am. B 20, 1503-1507 (2003)