The Nonaberrational Width of the Angular Spectrum of a Field Probing a Layered Object in Confocal Microscopy

Abstract

The influence of the numerical aperture of a light beam that probes a layered object on the magnitude of the quantity measured with a confocal interference microscope upon determining the object thickness has been studied theoretically and experimentally for the case in which the signal is significantly affected by the spherical aberration arising in the probing beam as it passes through the object. The dependence of the quantity to be measured on the numerical aperture is obtained taking into account the influence of the spherical aberration on the signal. The criterion of the “nonaberrational” propagation of the beam probing the object is determined and the condition under which the influence of the spherical aberration on the signal of the confocal microscope can be neglected is found. An approximate analytical expression is obtained, which makes it possible to determine the “nonaberrational” width of the angular spectrum of the light beam probing the object, taking into account an empirical correction factor. The applicability limits of the analytical dependence of the quantity to be measured on the numerical aperture, which has been previously obtained for the case of a negligibly weak influence of the spherical aberration on the signal from the confocal microscope, have been determined.