Scanning differential optical profilometer for simultaneous measurement of amplitude and phase variation

A scanning optical profilometer is described which can simultaneously and independently measure the differential phase/amplitude variation of light reflected off an object surface. This information may then be interpreted as topographical and reflectivity variation of the object surface. The system is based on a heterodyne interferometer and uses two beams to probe the surface. The theoretical sensitivity of the system is 3×10−3 mrad in phase and 3 in 105 in reflectivity variation, both measured in a 1 kHz bandwidth. Preliminary measurements of film thickness and reflectivity variation are presented. This system also has potential applications for imaging objects with minute structural variations.