Imaging with a High Numerical-Aperture Objective

So far, all our studies have been based on the paraxial approximation described in Section 2.4. This approximation holds for an imaging lens (objective) whose numerical aperture is not large, in which case many effects such as apodization, depolarization and aberration can be ignored. When the numerical aperture of a lens becomes approximately larger than 0.7, these effects become pronounced and must be included in the imaging theory. This chapter is devoted to the study of imaging with a high numerical-aperture objective. After the effects of a high numerical-aperture objective are described in Section 6.1, the Debye imaging theory for a high numerical-aperture objective, which has been mentioned in Section 2.3, is presented in Section 6.2. From the Debye theory, apodization, one of the effects related to a high numerical-aperture objective, is studied in detail in Section 6.3. Transfer functions under the Debye theory are derived in Section 6.4. The vectorial diffraction theory for a high numerical-aperture objective in a uniform medium is presented in Section 6.5. The focusing of a high numerical-aperture objective through dielectric interfaces is discussed in Section 6.6.