RESUMEN
Due to the diffraction limit, subwavelength nanoslits (whose width is strictly smaller than λ/2) are hard to resolve by optical microscopy. Here, we overcome the diffraction limit by measuring the full Stokes parameters of the scattered field of the subwavelength nanoslits with varying width under the illumination of a linearly-polarized laser with a 45° polarization orientation angle. Because of the depolarization effect arising from the different phase delay and amplitude transmittance for TM polarization (perpendicular to the long axis of slit) and TE polarization (parallel to the long axis of slit), the state of polarization (SOP) of the scattered light strongly depends on the slit width for subwavelength nanoslits. After correcting for residual background light, the nanoslit width measured by the SOP of scattered light is consistent with the scanning electron microscopy (SEM) measurement. The simulation and experiment in this work demonstrate a new far-field optical technique to determine the width of subwavelength nanoslits by studying the SOP of the scattered light.
RESUMEN
A pure longitudinal magnetization focal spot is greatly desired by all-optical magnetic recording. In this Letter, a triplex metalens is proposed and demonstrated to possess triple functions of an azimuthal polarization converter, a helical phase plate, and a focusing lens. The three-in-one combination enables conversion of linearly polarized incident light to the first-order azimuthally polarized vortex beam and focusing into a diffraction-limited spot. The state of polarization of the focal spot is measured to be pure circular polarization implying that a pure longitudinal magnetization field can be induced by the inverse Faraday effect. The lateral full width at half-maximum of the focal spot is 1.9 µm, and the experimental conversion efficiency of the metasurface is about 19.3%.
RESUMEN
To circumvent elaborate conventional lithographic methods for realizing metallic nanostructures, it is necessary to develop self-organized nanofabrication methods for suitable template structures and their optical characterization. We demonstrate the potential of ion bombardment with impurity co-deposition to fabricate terraced or quasi-blazed nanostructure templates. Self-organized terraced nanostructures on fused silica were fabricated using Ar+ ion bombardment with iron impurity co-deposition and subsequent Au shadow deposition. The aspect ratios are enhanced threefold, and the range of nanostructure period variation is significantly increased with respect to that of conventional nanostructures realized by pure ion bombardment. We reveal the key features of the method via atomic force microscopy and optical characterization. Variable-profile quasiperiodic nanostructures with periods of 100-450 nm, heights of 25-180 nm, and blaze angles of 10°-25° were fabricated over an area of 20×40mm2, and these exhibited tunable and broadening optical anisotropy across the nanostructured area. Thus, the proposed method is a viable technique for rapid, cost-effective, and deterministic fabrication of variable nanostructure templates for potential optical applications.
RESUMEN
Optical antennas enable efficient coupling between propagating light and bonding electromagnetic waves like surface plasmon polaritons (SPPs). Under the illumination of inhomogeneous optical fields, propagating SPPs mediated by multimode antennas could be spatially asymmetric and the asymmetry strongly depends on the position of the antennas relative to the illumination field. Here we develop such asymmetric excitation of SPPs through illuminating a pair of slot antennas with the (1,0) mode Hermite-Gaussian beam. The physical scenario of the interaction between the illumination optical field and the paired slot antennas are elaborated by full-wave electromagnetic simulations. We also carry out experiments to monitor the asymmetric SPPs propagation with a back-focal plane imaging technique. By retrieving the asymmetric intensity ratio of the SPP pattern in the back-focal plane image, lateral displacement of the antennas down to angstrom level is demonstrated.
RESUMEN
A long-range, high-precision, and compact transverse displacement metrology is of crucial importance in both industries and scientific researches. However, it is a great challenge to measure arbitrary two-dimensional (2D) displacement with angstrom-level precision and hundred-micrometer range. Here, we demonstrated a prototype of high-precision 2D-displacement metrology with matrix metasurface. Light passing through the metasurface is diffracted into three beams in horizontal (H), vertical (V), and diagonal (D) linear polarization. 2D transverse displacement of the metasurface relative to the incident light beam is retrieved from the interferential optical powers arisen from coherent superposition between H-polarized and D-polarized beams or V-polarized and D-polarized beams. We experimentally demonstrate that arbitrary displacement in 2D plane can be determined with high precision down to 0.3 nm in a large range of 200 micrometers. Our work broadens the application scope of metasurface and paves the way for development of ultrasensitive optical 2D displacement metrology.
RESUMEN
A long-range, high-precision, and compact transverse displacement metrology method is of crucial importance in many research areas. Recent schemes using optical antennas are limited in efficiency and the range of measurement due to the small size of the antenna. Here, we demonstrated the first prototype polarization-encoded metasurface for ultrasensitive long-range transverse displacement metrology. The transverse displacement of the metasurface is encoded into the polarization direction of the outgoing light via the Pancharatnam-Berry phase, which can be read out directly according to the Malus law. We experimentally demonstrate nanometer displacement resolution with the uncertainty on the order of 100 picometers for a large measurement range of 200 micrometers with the total area of the metasurface being within 900 micrometers by 900 micrometers. The measurement range can be extended further using a larger metasurface. Our work opens new avenues of applying metasurfaces in the field of ultrasensitive optical transverse displacement metrology.