The influence of the numerical aperture of a beam probing an object on the determination of the thickness of a layered object in confocal microscopy

The influence of the numerical aperture of a light beam probing an object on the value measured with a confocal interference microscope when determining the thickness of layered object has been theoretically and experimentally investigated. The dependence of the measured value on the numerical aperture in the form of an analytical formula is obtained. It is established that the measured value is determined by the average longitudinal spatial frequency of the field probing the object. The results of experimental verification of the dependence obtained allow us to conclude that it is possible to increase the measurement accuracy of geometrical thickness and refractive index of layered micro-objects by the methods of confocal microscopy.