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Opt Express. 2010 Mar 1;18(5):4518-25. doi: 10.1364/OE.18.004518.

Sub-wavelength focal spot with long depth of focus generated by radially polarized, narrow-width annular beam.

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  • 1Department of Electronic Science and Engineering, Kyoto University, Kyoto 615-8510, Japan.


We demonstrate the formation of a sub-wavelength focal spot with a long depth of focus using a radially polarized, narrow-width annular beam. Theoretical analysis predicts that a tighter focal spot (approximately 0.4 lambda) and longer depth of focus (more than 4 lambda) can be formed by a longitudinal electric field when the width of the annular part of the beam is decreased. Experimental measurements using a radially polarized beam from a photonic crystal laser agree well with these predictions. Tight focal spots with long depths of focus have great potential for use in high-tolerance, high-resolution applications in optical systems.

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