All-optical atom surface traps implemented with one-dimensional planar diffractive microstructures

We characterize the loading, containment and optical properties of all-optical atom traps implemented by diffractive focusing with one-dimensional (1D) microstructures milled on gold films. These on-chip Fresnel lenses with focal lengths of the order of a few hundred microns produce optical-gradient-dipole traps. Cold atoms are loaded from a mirror magneto-optical trap (MMOT) centered a few hundred microns above the gold mirror surface. Details of loading optimization are reported and perspectives for future development of these structures are discussed.Comment: 7 pages, 15 figure

Quantitative Determination of Enhanced and Suppressed Transmission through Subwavelength Slit Arrays in Silver Films

Measurement of the transmitted intensity from a coherent monomode light source through a series of subwavelength slit arrays in Ag films, with varying array pitch and number of slits, demonstrate enhancement (suppression) by as much as a factor of 6 (9) when normalized to that of an isolated slit. Pronounced minima in the transmitted intensity were observed at array pitches corresponding to lambda_SPP, 2lambda_SPP, and 3lambda_SPP where lambda_SPP is the wavelength of the surface plasmon polariton (SPP). Increasing the number of slits to more than four does not increase appreciably the per-slit transmission intensity. These results are consistent with a model for interference between SPPs and the incident wave that fits well the measured transmitted intensity profile.Comment: Figure 4 update

Surface-wave-enabled darkfield aperture for background suppression during weak signal detection

Sensitive optical signal detection can often be confounded by the presence of a significant background, and, as such, predetection background suppression is substantively important for weak signal detection. In this paper, we present a novel optical structure design, termed surface-wave-enabled darkfield aperture (SWEDA), which can be directly incorporated onto optical sensors to accomplish predetection background suppression. This SWEDA structure consists of a central hole and a set of groove pattern that channels incident light to the central hole via surface plasmon wave and surface-scattered wave coupling. We show that the surface wave component can mutually cancel the direct transmission component, resulting in near-zero net transmission under uniform normal incidence illumination. Here, we report the implementation of two SWEDA structures. The first structure, circular-groove-based SWEDA, is able to provide polarization-independent suppression of uniform illumination with a suppression factor of 1230. The second structure, linear-groove-based SWEDA, is able to provide a suppression factor of 5080 for transverse-magnetic wave and can serve as a highly compact (5.5 micrometer length) polarization sensor (the measured transmission ratio of two orthogonal polarizations is 6100). Because the exact destructive interference balance is highly delicate and can be easily disrupted by the nonuniformity of the localized light field or light field deviation from normal incidence, the SWEDA can therefore be used to suppress a bright background and allow for sensitive darkfield sensing and imaging (observed image contrast enhancement of 27 dB for the first SWEDA)

Universal optical transmission features in periodic and quasiperiodic hole arrays

We investigate the influence of array order in the optical transmission properties of subwavelength hole arrays, by comparing the experimental spectral transmittance of periodic and quasiperiodic hole arrays as a function of frequency. We find that periodicity and long-range order are not necessary requirements for obtaining enhanced and suppressed optical transmission, provided short-range order is maintained. Transmission maxima and minima are shown to result, respectively, from constructive and destructive interference at each hole, between the light incident upon and exiting from a given hole, and surface plasmon polaritons (SPPs) arriving from individual neighboring holes. These SPPs are launched along both illuminated and exit surfaces, by diffraction of the incident and emerging light at the neighboring individual subwavelength holes. By characterizing the optical transmission of a pair of subwavelength holes as a function of hole-hole distance, we demonstrate that a subwavelength hole can launch SPPs with an efficiency up to 35%, and with an experimentally determined launch phase φ = π/2, for both input-side and exit-side SPPs. This characteristic phase has a crucial influence on the shape of the transmission spectra, determining transmission minima in periodic arrays at those frequencies where grating coupling arguments would instead predict maxima

Surface-wave interferometry on single subwavelength slit-groove structures fabricated on gold films

We apply the technique of far-field interferometry to measure the properties of surface waves generated by two-dimensional (2D) single subwavelength slit-groove structures on gold films. The effective surface index of refraction measured for the surface wave propagating over a distance of more than 12 microns is determined to be 1.016 with a measurement uncertainty of 0.004, to within experimental uncertainty of the expected bound surface plasmon-polariton (SPP) value for a Au/Air interface of 1.018. We compare these measurements to finite-difference-time-domain (FDTD) numerical simulations of the optical field transmission through these devices. We find excellent agreement between the measurements and the simulations for the surface index of refraction. The measurements also show that the surface wave propagation parameter exhibits transient behavior close to the slit, evolving smoothly from greater values asymptotically toward the value expected for the SPP over the first 2-3 microns of slit-groove distance. This behavior is confirmed by the FDTD simulations

Loss mechanisms of surface plasmon polaritons on gold probed by cathodoluminescence imaging spectroscopy

We use cathodoluminescence imaging spectroscopy to excite surface plasmon polaritons and measure their decay length on single crystal and polycrystalline gold surfaces. The surface plasmon polaritons are excited on the gold surface by a nanoscale focused electron beam and are coupled into free space radiation by gratings fabricated into the surface. By scanning the electron beam on a line perpendicular to the gratings, the propagation length is determined. Data for single-crystal gold are in agreement with calculations based on dielectric constants. For polycrystalline films, grain boundary scattering is identified as additional loss mechanism, with a scattering coefficient SG=0.2%

Electrooptic Modulation in Thin Film Barium Titanate Plasmonic Interferometers

We demonstrate control of the surface plasmon polariton wavevector in an active metal−dielectric plasmonic interferometer by utilizing electrooptic barium titanate as the dielectric layer. Arrays of subwavelength interferometers were fabricated from pairs of parallel slits milled in silver on barium titanate thin films. Plasmon-mediated transmission of incident light through the subwavelength slits is modulated by an external voltage applied across the barium titanate thin film. Transmitted light modulation is ascribed to two effects, electrically induced domain switching and electrooptic modulation of the barium titanate index

Coupling of spontaneous emission from GaN/AlN quantum dots into silver surface plasmons

We have demonstrated surface-plasmon induced change in spontaneous emission rate in the ultraviolet regime at ~ 375-380 nm, using AlN/GaN quantum dots (QD). Using time-resolved and continuous-wave photoluminescence measurements, the recombination rate in AlN/GaN QD is shown to be enhanced when spontaneous emission is resonantly coupled to a metal-surface plasmon mode. The exciton recombination process via Ag-surface plasmon modes is observed to be as much as 3-7 times faster than in normal QD spontaneous emission and depends strongly on the emission wavelength and silver thickness.Comment: 11 pages, 4 figure

Negative Refraction at Visible Frequencies

Nanofabricated photonic materials offer opportunities for crafting the propagation and dispersion of light in matter. We demonstrate an experimental realization of a two-dimensional negative-index material in the blue-green region of the visible spectrum, substantiated by direct geometric visualization of negative refraction. Negative indices were achieved with the use of an ultrathin Au-Si_3N_4-Ag waveguide sustaining a surface plasmon polariton mode with antiparallel group and phase velocities. All-angle negative refraction was observed at the interface between this bimetal waveguide and a conventional Ag-Si_3N_4-Ag slot waveguide. The results may enable the development of practical negative-index optical designs in the visible regime