## Abstract

The dyadic Green’s function (DGF) is applied to examine the effect of focal shift in
a spherical microlens with the variation of the numerical aperture for a given
Fresnel number when a monochromatic plane wave with *x* linear
polarization is incident on the microlens. By comparing the results based on the
method for the vector Kirchhoff diffraction theory [J. Opt. Soc. Am. A **22**, 68–76
(2005)], the effect of the
spherical aberration on focal shift in a microlens is evaluated, and the influences
of NA as well as the spherical aberration on the transverse electric energy density
distribution in the focal plane are also investigated. In contrast with other vector
formulations of imaging theory, which mainly focus on the focal shift in an aplanatic
system, the DGF method is more practical and effective to locate the principal
maximum energy density along the normal axis and to study transverse electric energy
density distribution, because the actual shape of a microlens and the effects of
aberrations are considered.

© 2009 Optical Society of America

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