When a linearly polarized plane wave is focused by a diffraction-limited lens, according to the scalar theory, the intensity in the focal plane is given by the well-known Airy pattern. But for a lens with large numerical aperture, the scalar theory is not accurate and one should apply the vector diffraction theory to obtain the field distribution in the focal region. In the case of a linearly polarized plane wave focused by a diffraction-limited lens of high numerical aperture, the vector theory of diffraction yields the so-called "vectorial Airy pattern".

For many applications such as laser writing, optical recording, confocal microscopy and lithography, a very sharp spot is desired, i.e., an amplitude distribution that is peaked at the optical axis. In other applications such as imaging single molecules, fluoresecence microscopy and optical trapping, also the optimization of the polarization direction of electric field in focus can be important.

In this talk, we discuss the optimization of the distribution of the electric field (amplitude, phase and polarization) in the focal area by shaping the field distribution at the input pupil. We also consider the situation where the spot size is compressed further by adding a superresolution layer in the focal region.

Simulations and experimental results of direct measurements of the focused field using a near-field scanning microscope will be shown as well as applications in research and industry.


Seminar, March 9, 2012, 15:00. Seminar Room

Hosted by Prof. Niek van Hulst