Subwavelength-resolvable focused non-Gaussian beam shaped with a binary diffractive optical element

The diffraction-limited spot size limits the optical disk storage capacity and microscopic resolution. We describe a technique to shape a focused Gaussian beam into a superresolving beam by using a diffractive optical element fabricated by laser-assisted chemical etching. The focused shaped beam has a smaller width and a longer depth of focus than a similarly focused Gaussian beam. Using the diffraction-limited shaped beam along with threshold writing, we achieved a written pit size of less than 0.33 μm at a 695-nm laser wavelength, compared with a 0.7-μm focused Gaussian spot size (full width at e^-2 of the peak) with the same focusing lens. The energy conversion efficiency for the beam shaping was ∼81%.