Masud Mansuripur, Lifeng Li, Wei-Hung Yeh
Diffraction-limited focusing of a laser beam for the purpose of scanning a surface to either explore or modify that surface is the basis of several important technologies. Examples include scanning optical microscopy, optical disk data storage, and laser printing. The size of the focused spot and the corresponding depth of focus are important factors in determining the performance characteristics of these systems. This month's column is part one of a two-part series that examines methods of forming the focused spot, and attempts to clarify the relation between the spot size and the depth of focus. The first part addresses imaging through air, immersion oil, and cover plates. Next month's column will continue this discussion, concentrating on imaging through solid immersion lenses.
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