Phase conjugation of optical dipole fields is considered in a static holographic scheme with totally internally reflected reference and reconstruction waves. It is shown that as the distance between the dipole object and the recording medium decreases from the far-to the near-field region, the intensity distribution of the reconstructed dipole field changes from a diffraction-limited light spot to a subwavelength-sized light spot that is brightest at the surface of the hologram. The influence of the thickness of the recording medium, the angle of incidence of the reconstruction wave, and the polarization configuration on the reconstructed intensity distribution are also discussed.
We study how a converging spherical wave gets distorted by a plane dielectric interface. The fields in the second medium are obtained by evaluating the m-theory diffraction integral on the interface. The loss of intensity and the form of the intensity distribution are investigated. Examples are presented for various refractive-index contrasts and depths of focus. In general the intensity gets spread out over a volume that is large compared with the case without refractive-index contrast. It was found that moving the focusing lens a distance d toward the interface does not result in an equal shift of the intensity profile. This latter point has important practical implications.
Using the electromagnetic equivalent of the Kirchhoff diffraction integral, we investigate the effect of spherical aberration and defocus on the diffraction of Gaussian, uniform, and centrally obscured beams. We find, among other things, that in high-angular-aperture systems suffering from either spherical aberration or defocus the axial intensity distribution is no longer symmetric. Equations are derived for the axial intensity near focus for different beam profiles. Intensity contours in focal and meridional planes are depicted for both ideal and aberrated lenses. It is shown that, contrary to certain previous theories, our theory is valid for both high and low angular aperture systems. INTRODUCTIONIn a previous paper' we have given a detailed description of a new electromagnetic diffraction theory based on the vectorial equivalent of the Kirchhoff-Fresnel integral. The diffracted fields were obtained by integration over the (aberrated) wave front. We applied this theory to investigate the effect of spherical aberration on the electromagnetic field in the focal region of a high-aperture lens. Among other things, we found for an incoming plane wave that the intensity distribution on the axis was no longer symmetric around the peak. A similar feature has recently been measured. 2 Our aim in the present paper is twofold. First, we show that the vectorial theory of Richards and Wolf, 3 4 which is valid for high-aperture values, and the paraxial scalar theory of Li and Wolf' are both special cases of our approach. Second, we extend this electromagnetic model to include Gaussian beams, centrally obscured beams, and defocus. Equations are derived for the axial intensity distribution of such systems. It was found for high-aperture lenses with defocus that the displacement theorem (Ref. 6, Chap. 9), which predicts a mere shift of the diffraction pattern, no longer holds. The intensity distribution is now asymmetric and has a lower peak intensity.It is seen in our study that one can clearly distinguish among three types of lens, namely, paraxial, lowaperture, and high-aperture systems, with Fresnel numbers of order 1, 102, and 104, respectively.A study of different beam profiles, but for a scalar theory in the Fresnel approximation, has been carried out by Mahajan, 7 who compared beams with the same total power. We also mention the research of Mansuripur, who describes a vectorial Fresnel diffraction theory. It should be noted that these Fresnel theories are based on four additional assumptions that are not present in our framework:
We present a model for investigating the effect of spherical aberration on the electromagnetic field and the Poynting vector in the focal region of a high-aperture lens. The fields are obtained by integrating the vector equivalent of Kirchhoff's boundary integral over the aberrated wave front. We have studied both diffraction patterns and transfer functions. Our results differ significantly from those obtained by classical focusing theory. For example, the intensity peak is narrower. Also the intensiy distribution is no longer symmetric on the optical axis. A similar asymmetry has recently been measured.
Using an electromagnetic approach, we calculate the properties of a confocal fluorescence microscope. It is expected that the results will be more reliable than those obtained by conventional scalar theory, the results of which differ significantly from ours. We calculate the point-spread function and the optical transfer function and study the influence of detector size and fluorescence wavelength on the optical sectioning capability. Our calculations are based on electromagnetic diffraction theory in the Debye approximation. The recently noted asymmetry between the illumination and the detection sensitivity distribution is also taken into account.
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