Interfacial shape and contact-angle measurement of transparent samples with confocal interference microscopy

A model has been developed that predicts the effective optical path through a thick, refractive specimen on a reflective substrate, as measured with a scanning confocal interference microscope equipped with a high-numerical-a perture objective. Assuming that the effective pinhole of the confocal micr oscope has an infinitesimal diameter, only one ray in the illumination bund le (the magic ray) contributes to the differential optical path length (OPL ). A pinhole with finite diameter, however, allows rays within a small angu lar cone centered on the magic ray to contribute to the OPL. The model was incorporated into an iterative algorithm that allows the measured phase to be corrected for refractive errors by use of an a priori estimate of the sa mple profile. The algorithm was validated with a reflected-light microscope equipped with a phase-shifting laser-feedback interferometer to measure th e interface shape and the 68 degrees contact angle of a silicone-oil drop o n a coated silicon wafer. (C) 2000 Optical Society of America. OCIS codes: 120.3180, 170.1790, 180.3170, 120.3940, 120.2830.