Performance parameters for highly-focused electromagnetic waves |
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Authors: | Colin JR Sheppard Naveen K Balla Shakil Rehman |
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Institution: | a Division of Bioengineering, National University of Singapore, 9 Engineering Drive 1, Singapore 117576, Singapore b Department of Diagnostic Radiology, National University of Singapore, 5 Lower Kent Ridge Road, Singapore 119074, Singapore c Computation and Systems Biology, Singapore-MIT Alliance, National University of Singapore, Singapore 117576, Singapore |
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Abstract: | New performance parameters are presented for electromagnetic focusing systems of high numerical aperture. The field in the focal region is expanded into either electric/magnetic dipole components, or transverse electric/magnetic components. The treatments can be applied to the important case of electric dipole waves, where the focused polarization distribution is the same as that of an electric dipole. For the limiting case of a system of unity numerical aperture, the transverse focus for a focused electric dipole field is sharpened up by 19% compared with an aplanatic system with plane-polarized input, while at the same time the focal intensity for a given input power is increased by 17%. This should be contrasted with using a pupil filter, in which case, as the focal spot is made smaller the focal intensity also decreases. Pure TE polarization results in an even smaller central lobe. Other inhomogeneous polarizations can also be investigated as linear combinations of electric/magnetic or TE/TM components. |
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Keywords: | 100 6640 110 1220 140 3300 350 5730 |
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