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Schematic images of focused radially polarized beams and their calculated intensity profiles near the focal plane (z/λ = 0) for the case of NA = 0.9. Black arrows show the electrical polarization. The electrical vectors passing through the lens can be resolved into transverse and longitudinal components. The longitudinal components constructively interfere at the beam axis near the focal plane. For a conventional doughnut-shaped beam (a), the inner part of the beam generates more intense transverse components than longitudinal components, whereas the outer part of the beam generates more intense longitudinal components than transverse components. For a halo-shaped beam (b) with a ratio of the inner to outer ring radius between 0.9 and 1, the longitudinal components dominate.
(a) Schematic image of the photonic crystal ring-cavity laser constructed in the current study. (b) Scanning electron microscopy image of the photonic crystal layer. The depth of the ditches is 100 nm. The air-filling factor of the quasi-one-dimensional lattice points is designed to be 40%. (c)Electromagnetic field associated with one asymmetric lattice point of the photonic crystal. The black arrows show electric polarization. (d) The asymmetric lattice points are arranged such that they diffract with radial polarization in the vertical direction of the cavity.
Lasing properties of photonic crystal ring-cavity laser. (a) Near-field image and distribution of spectra under the pulsed condition at room temperature. (b) Far-field image. (c) Polarization.
Focusing properties of photonic crystal ring-cavity laser. (a) Experimental set-up for investigating focusing properties. (b) Results for radially polarized halo-shaped beam. (c) Results for radially polarized doughnut-shaped beam. The maximum intensity at z = +2.5 μm is five times larger than that at z = 0, and the maximum intensity at z = +5 μm is ten times larger than that at z = 0. (d) Comparison of experimental and calculated depth of focus for the two beam types.
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