Measurement techniques to determine the aberration of an optical system, by obtaining through-focus intensity
images that are produced when the object is a point source at infinity, are shown. The analysis of the aberrations
is made using the extended version of the Nijboer-Zernike diffraction theory. This theory provides a semi
analytical solution of the Debye diffraction integral and thus a direct relation between the intensity distribution
of the field at the focal region and the exit pupil of the optical system.
We propose a measurement approach that allows the determination of aberrations of a microlens by analyzing
the through-focus intensity image it produces when the object is a point source. To simulate image formation by
a microlens we apply the extended version of the Nijboer-Zernike diffraction theory (ENZ) that uses the Debye
diffraction integral to compute the image point-spread function. Due to the aperture size of the microlens and
the finite dimensions of the pixels of the electronic detector the Debye diffraction integral should be adapted
according to the Li-Wolf scaling rules to yield correct results. In addition to this we also discuss the experimental
requirements posed by this characterization approach and derive from this a suitable experimental setup.
In this paper we introduce a new mask imaging algorithm that is based on the source point integration method
(or Abbe method). The method presented here distinguishes itself from existing methods by exploiting the
through-focus imaging feature of the Extended Nijboer-Zernike (ENZ) theory of diffraction. An introduction
to ENZ-theory and its application in general imaging is provided after which we describe the mask imaging
scheme that can be derived from it. The remainder of the paper is devoted to illustrating the advantages of the
new method over existing methods (Hopkins-based). To this extent several simulation results are included that
illustrate advantages arising from: the accurate incorporation of isolated structures, the rigorous treatment of the
object (mask topography) and the fully vectorial through-focus image formation of the ENZ-based algorithm.
Results are presented of mask imaging using the Extended Nijboer-Zernike (ENZ) theory of diffraction. We
show that the efficiency of a mask imaging algorithm, derived from this theory, can be increased. By adjusting
the basic Finite Difference Time Domain (FDTD) algorithm, we can calculate the near field of isolated mask
structures efficiently, without resorting to periodic domains. In addition, the calculations for the points on the
entrance sphere of the imaging system can be done separately with a Fourier transformed Stratton-Chu nearto-
far-field transformation. By clever sampling in the radial direction of the entrance pupil, the computational
effort is already reduced by at least a factor of 4.
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