Tight focus of light using micropolarizer and microlens.

ABSTRACT

Using a binary microlens of diameter 14 µm and focal length 532 nm (NA=0.997) in resist, we focus a 633 nm laser beam into a near-circular focal spot with dimensions (0.35 ± 0.02)λ and (0.38 ± 0.02)λ (λ is incident wavelength) at full width half-maximum intensity. The area of the focal spot is 0.105λ(2). The incident light is a mixture of linearly and radially polarized beams generated by reflecting a linearly polarized Gaussian beam at a 100 µm × 100 µm four-sector subwavelength diffractive optical microelement with a gold coating. The focusing of a linearly polarized laser beam (the other conditions being the same) is found to produce an elliptical focal spot measuring (0.40 ± 0.02)λ and (0.50 ± 0.02)λ. To our knowledge, this is the first implementation of subwavelength focusing of light using a pair of micro-optic elements (a binary microlens and a micropolarizer).