Sjoerd H. Wiersma

Comparison of different theories for focusing through a plane interface

We consider the problem of light focusing by a high-aperture lens through a plane interface between two media with different refractive indices. We compare two recently published diffraction theories and a new geometrical optics description. The two diffraction approaches exhibit axial distributions with little difference. The description based on geometrical optics is shown to agree well with the diffraction optics results. Also, some implications for three-dimensional imaging are discussed.

Defocusing of a converging electromagnetic wave by a plane dielectric interface

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.

Spherical aberration and the electromagnetic field in high-aperture systems

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.

Annular focusing through a dielectric interface: scanning and confining the intensity

We study the problem of light focusing by a high-aperture lens through a planar interface between two media with different refractive indices. It is demonstrated how, by using annular illumination, the intensity distribution can be significantly confined. A new scanning mechanism is proposed to continuously probe the intensity peak through the second medium. This mechanism may be applied in, for example, lithography and three-dimensional imaging.

Focusing through an interface:?scanning and localizing the intensity

Focusing light through an interface leads to an aberrated intensity distribution that is highly extended with a relatively low peak intensity. We present a method, using a well-chosen annular aperture, that can greatly improve the localization of the intensity about a prescribed point on the axis. Also, the intensity at that point can be increased significantly. By continuously varying the annulus radii, we can scan the intensity peak through the second medium. This localization and scanning method has possible applications in three-dimensional imaging and lithography.