Conversion of evanescent into propagating light in near-field scanning optical microscopy

Conversion of evanescent light into propagating light (as needed in near-field scanning optical microscopy) is analyzed by means of a photocantilever. The photocantilever is a silicon cantilever with a pn junction photodiode on its tip. The photocantilever tip converts evanescent light from a sample into propagating light. Theoretical values given by scattering and transmission models are compared with our experimental values. The scattering model gives results that are closer to the experimental values than does the transmission model. This indicates that the nonpropagating evanescent light is converted into scattered light at the photocantilever tip, and that the scattered light is collected by the photodiode. (C) 1996 American Institute of Physics.