Method and apparatus for measuring the flatness of the roughness or of the curvature radius the measuring surface

摘要

Two radiation components differing from each other with regard to their state of polarization or their wavelength are directed onto closely adjacent points of the object to be measured. The reflected components are recombined and are fed to a polarization- or wavelength-dependent phase shifter periodically shifting the phase positions of the two components by lambda /2 against each other. A phase shift of one of the components caused by the object to be measured is fully compensated for by periodically shifting the phase position of the other component at particular points in time, which can be determined, for example, by means of a connected analyzer and a photodetector. The values of the control voltage effecting the periodical phase shift in the phase shifter are measured at those points in time at which the phase difference between the two components equals zero. These values are proportional to the difference in height between the points of incidence of the two radiation components on the object surface or the slope of the object surface.