Effect of the Number of Zones in a One-Dimensional Plasmonic Zone Plate Lens: Simulation and Experiment

A 1D plasmonic zone plate lens (PZPL) consisting of nano-slits within a metal film introduces a phase delay distribution across the planar device surface by a modulation of the slit widths and positions to achieve light focusing. Using the finite-difference time-domain method, the number of zones is found to be a crucial factor for a well-controlled focal length, i.e. at least three zones are necessary for a PZPL exhibiting a focal length in agreement with the design. This conclusion is confirmed by confocal scanning optical microscopy on PZPLs patterned in an aluminium film. In addition, subwavelength light focusing is demonstrated both theoretically and experimentally in a PZPL. A larger PZPL, i.e. more zones, shows a higher resolution. A full full-width half-maximum of 0.37λ in the focal plane is shown theoretically in a PZPL with seven zones. A comparison between the PZPL and the plasmonic Fresnel zone plate shows that PZPLs have a higher contrast at the focus.     

High Efficient Far-Field Nanofocusing with Tunable Focus Under Radial Polarization Illumination

We design a new nanofocusing lens for far-field practical applications. The constructively interference of cylindrical surface plasmon launched by the subwavelength metallic structure can form a subdiffraction-limited focus, which is modulated by the dielectric grating from the near field to the far field. The principle of designing such a far-field nanofocusing lens is elucidated in details. The numerical simulations demonstrated that nanoscale focal spot (0.12λ ²) can be realized with 3.6λ in depth of focus and 4.5λ in focal length by reasonably designing parameters of the grating. The focusing efficiency can be 7.335, which is much higher than that of plasmonic microzone plate-like lenses. A blocking chip can enhance the focusing efficiency further as the reflected waves at the entrance would be recollected at the focus. By controlling the number of the grooves in the grating, the focal length can be tuned easily. This design method paved the road for utilizing the plasmonic lens in high-density optical storage, nanolithography, superresolution optical microscopic imaging, optical measurement, and sensing.     

Robustly Efficient Superfocusing of Immersion Plasmonic Lenses Based on Coupled Nanoslits

We report plasmonic lenses consisting of coupled nanoslits immersed in a high-index medium to obtain the robustly efficient superfocusing. Based on the geometrical optics and the wavefront reconstruction theory, an array of nanoslits perforated in a gold film and a series of spacings between adjacent nanoslits are optimally designed to realize the desired phase modulation for light focusing. The numerical results verify the design of each plasmonic lens in excellent agreement. For the given total phase difference of 2π, the immersion plasmonic lenses with smaller lens aperture can have much better focusing performance than the non-immersion one. A superfocusing spot of λ/4.39 is achieved using an oil immersion plasmonic lens with an aperture size of 4.97λ, resulting in a resolution improvement of 68.9 % compared with the non-immersion lens. Moreover, such superfocusing performance can be still well kept when the structural parameters of the lens, e.g., nanoslit width and metal film thickness, are deviated from the original design, making the final implementation of the superfocusing lenses much easier.     

An Annular Plasmonic Lens Under Illumination of Circularly Polarized Light

In this paper, we consider a circular central aperture surrounded with annular depth-tuned grooves and investigate the beaming effect of the structure under illumination of a circularly polarized (CP) plane wave. As a CP plane wave is equivalent to the superposition of two linearly polarized plane waves (TM and TE) with a phase difference of π/2, the superposition of the electric field intensity, ( | E_x |² + | E_y |² ) \left( {{{\left| {E_x} \right|}^2} + {{\left| {E_y} \right|}^2}} \right) , is observed in the transmission field. In addition, two plasmonic modes are found at the resonant wavelengths λ ₁ and λ ₂ with each consisting of multiple wavelengths. At the wavelength λ ₁ = 420 nm, the significant near-field collimation is formed along the direction z, having a long propagation distance up to 1.75 μm (≈4λ) away from the exit plane of the new plasmonic lens.     

Finite element modeling of arachnid slit sensilla—I. The mechanical significance of different slit arrays

Arachnid strain sensitive slit sensilla are elongated openings in the cuticle with aspect ratios (slit length l / slit width b) of up to 100. Planar Finite Element (FE) models are used to calculate the relative slit face displacements, D _c, at the centers of single slits and of arrangements of mechanically interacting slits under uni-axial compressive far-field loads. Our main objective is to quantitatively study the role of the following geometrical parameters in stimulus transformation: aspect ratio, slit shape, geometry of the slits‘ centerlines, load direction, lateral distance S, longitudinal shift λ, and difference in slit length Δl between neighboring slits. Slit face displacements are primarily sensitive to slit length and load direction but little affected by aspect ratios between 20 and 100. In stacks of five parallel slits at lateral distances typical of lyriform organs (S = 0.03 l) the longitudinal shift λ substantially influences slit compression. A change of λ from 0 to 0.85 l causes changes of up to 420% in D _c. Even minor morphological variations in the arrangements can substantially influence the stimulus transformation. The site of transduction in real slit sensilla does not always coincide with the position of maximum slit compression predicted by simplified models. An erratum to this article can be found at     

A Design Method for a Micron-Focusing Plasmonic Lens Based on Phase Modulation

A design method of a micron-focusing plasmonic lens is proposed, which consists of a nanoaperture surrounded by concentric annular grooves with fixed width and depth. The phase modulation of the radiation lights decoupled from surface plasmon polariton waves by the annular grooves is realized by altering the radii of the grooves. Based on the principle of the constructive interference, a design formula of a micron-focusing plasmonic lens is deduced. The transmitted fields through the designed plasmonic lenses are numerically simulated with finite-difference time-domain method, and the results show that a circular focusing spot is generated where the focal length can be controlled in several micrometers, which agree with our theoretical analysis.     

Simulation and Analytical Study of Optical Complex Field in Nano-corral Slits Plasmonic Lens

Although spiral plasmonic lens has been proposed as circular polarization analyzer, there is no such plasmonic nanostructure available for linear polarization. In the current work, we have designed nano-corral slits (NCS) plasmonic lens, which focuses the x- and y-polarized light into spatially distinguished plasmonic fields. We have calculated analytically and numerically the electric field intensity and phase of the emission from nano-corral slits plasmonic lens with different pitch lengths under various polarizations of the illumination. It has been shown that one can control the wave front of the output beam of these plasmonic lenses by manipulating the illumination of both circular and linear polarization. Our theoretical study in correlation with FDTD simulation has shown that NCS plasmonic lens with pitch length equal to λ_spp produces scalar vortex beam having optical complex fields with helical wave front and optical singularity at the center under circular polarization of light. When NCS lens (pitch = λ_spp) is illuminated with linearly polarized light, it exhibits binary distribution of phase with same electric field intensity around the center. However, with pitch length of 0.5λ_spp, NCS shows linear dichroism under linearly polarized illumination unlike spiral plasmonic lens (SPL) eliminating the use of circularly polarized light. Optical complex fields produced by these NCS plasmonic lenses may find applications for faster quantum computing, data storage, and telecommunications.

     

Computational Study of Influence of Structuring of Plasmonic Nanolens on Superfocusing

The focusing effect of the plasmonic nanolens is studied systematically. The influence of different construction parameters including the size of the central hole, the ring width of the surrounding concentric grating, the thickness of the metal film, and the distance of the central hole to grating has been simulated by rigorous finite difference time domain method and analyzed. It is found that the intensity of the central nano-spot is linearly proportional to the size of the central hole and inversely linearly proportional to the thickness of the metal film. In addition, the intensity of the lobes can be suppressed effectively by reducing the ring width down to a quarter of plasmon wavelength to achieve a better focusing effect. The influence of the distance of central hole to grating is a little bit complex, but generally, the intensity for the distance of (2n − 1)/2 plasmon wavelength is larger than the case of the distance of nλ_SP. The simulation results can be a general guide for the design of plasmonic nanolenses.     

Hybrid Dielectric-Loaded Plasmonic Waveguide-Based Power Splitter and Ring Resonator: Compact Size and High Optical Performance for Nanophotonic Circuits

The key challenge of the plasmonic waveguide is to achieve simultaneously both the long propagation length and high confinement. The hybrid dielectric-loaded plasmonic waveguide consists of a SiO₂ stripe sandwiched between a Si-nanowire and a silver film and thus promises as a best candidate to overcome this challenge. We propose to exploit this unique property of this structure to design different high-efficient silicon-based plasmonic components including waveguide, power splitter, and wavelength-selective ring resonator. As a result, the proposed power splitter with a waveguide cross section (λ ²/60) and a strong mode confinement area (~λ ²/240) features a low power transmission loss (<0.4 dB) at the optimal arm length of 4 μm with respect to different separation distances of output arms. Moreover, we also demonstrate that a plasmonic ring resonator with a compact ring radius of 2 μm may achieve high optical performance such as high-extinction ratio of 30 dB, large free spectral range of 67 nm, and small bandwidth of 0.6 nm. These superior performances make them promising building blocks for integrated nanophotonic circuits.     

Active Focal Length Control of Terahertz Slitted Plane Lenses by Magnetoplasmons

Active plasmonic devices are mostly designed at visible frequencies. Here, we propose an active terahertz (THz) plasmonic lens tuned by an external magnetic field. Unlike other tunable devices where the tuning is achieved by changing the plasma frequency of materials, the proposed active lens is tuned by changing the cyclotron frequency through manipulating magnetoplasmons (MPs). We have theoretically investigated the dispersion relation of MPs of a semiconductor?Cinsulator?Csemiconductor structure in the Voigt configuration and systematically designed several lenses realized with a doped semiconductor slab perforated with sub-wavelength slits. It is shown through finite?Cdifference time?Cdomain simulations that THz wave propagating through the designed structure can be focused to a small size spot via the control of MPs. The tuning range of the focal length under the applied magnetic field (up to 1?T) is ??3??, about 50% of the original focal length. Various lenses, including one with two focal spots and a tunable lens for dipole source imaging, are realized for the proposed structure, demonstrating the flexibility of the design approach. The proposed tunable THz plasmonic lenses may find applications in THz science and technology such as THz imaging.     

Plasmonic Band Gap: Role of the Slit Width in 1D Metallic Grating on Higher Refractive Index Substrate

This paper reports the excitation of surface plasmon polaritons (SPPs) and associated plasmonic band gap (PBG) while using TM plane wave interacting with 1D metallic grating on higher refractive index GaP substrate. A simple method is introduced to estimate the PBG which is crucial for many plasmonic devices. The PBG is estimated by measuring the transmission spectra obtained through the plasmonic grating structures when slit width is varied while periodicity and the thickness of the gold (Au) film remained fixed. The PBG is observed for the grating devices whose slit width is less than one third of the periodicity which is caused by the presence of a higher plasmonic mode. The PBG is absent for the grating device whose slit width is slightly less than half and greater than one third of the periodicity. Such grating devices support only a fundamental plasmonic mode because the profile/shape of the slit in the grating device is more like a sinusoidal nature. Furthermore, such grating offers intermediate scattering to the incident light and the SPP as well which in turn couple more incident energy to the SPPs. Far-field modelling results also support the results obtained through experiment.

     

Shifts in the semidian rhythm of flowering do determine night-break timing and critical night length in Pharbitis nil

There is a semidian (≈12 h) rhythm in the flowering response of the short-day plant Pharbitis nil Choisy following 90 min exposure to either far-red light/darkness or a temperature drop (27 °C to 12 °C) given at various times in constant conditions before an inductive dark period. This semidian rhythmic response to the temperature-drop pretreatments in the light is also evident through the inductive dark period without change of phase. Furthermore, those pretreatments which increase flowering also advance the time of maximum sensitivity to red light (R) interruptions of the dark period by up to 1.5 h and shorten the critical night length. Conversely, pretreatments which reduce flowering delay the time of maximum R inhibition by up to 1.5 h and increase the critical night length by the same amount. However the phase of a circadian rhythm of flowering response had no effect on either the time of maximum R inhibition or the critical night length. Thus, the semidian rhythm determines both the time of maximum R inhibition and the critical night length in Pharbitis. Received: 8 November 1997 / Accepted: 7 January 1998     

Super-Resolution Long-Depth Focusing by Radially Polarized Light Irradiation Through Plasmonic Lens in Optical Meso-field

In this paper, we propose a novel plasmonic lens design consisting of an annular slit and concentric grooves. The simulation results show that under radially polarized illumination, a super-resolution long depth of focus (DOF) spot can be achieved in optical meso-field due to the constructive interference of scattered light by the concentric grooves. We also analyze the influence of depth-tuned annular grooves on focusing performance, including focal length, DOF, and full-width half-maximum. Moreover, focusing efficiency can be enhanced (～350 %) by introducing a circular metallic grating which surrounds the annular slit. This plasmonic lens has potential applications in nano-imaging and nano-photolithography.     

Near-infrared Plasmonic Far-field Nanofocusing Effects with Elongated Depth of Focus based on Hybrid Au–Dielectric–Ag Subwavelength Structures

In this paper, we propose a new far-field nanofocusing lens with elongated depth of focus (DOF) under near-infrared (NIR) wavelength. The surface plasmons can be excited by using the hybrid metal–insulator–metal (MIM) subwavelength structure under the NIR wavelength. The constructive interference of surface plasmons launched by the subwavelength MIM structure can form a nanoscale focus that is modulated by the novel metal grating from the near field to the far field. The numerical simulations demonstrated that a nanoscale focal spot (in plane focal area 0.177λ ²) with elongated DOF (3.358λ) and long focal length (5.084λ) can be realized with reasonably designing parameters of the lens. By controlling the positions of the inner radii of each slit ring and the grating width, the focal length, focal spot, and DOF can be tuned easily. This design method, which can obtain the nanoscale focal spot and micron DOF in far field under NIR illumination, paved the road for utilizing the NIR plasmonic lens in superresolution optical microscopic imaging, optical trapping, biosensing, and complex wavefront/beam shaper.     

Subwavelength Focusing Using Plasmonic Wavelength-Launched Zone Plate Lenses

We propose a plasmonic wavelength-launched Fresnel zone plate structure for subwavelength focusing. The plasmonic structure consists of a central circular groove surrounded by 12 transparent and opaque zones. All the zones with widths smaller than one half of the incident wavelength are used to enhance the field of evanescent waves in the transmission. Based on the finite-difference time-domain analysis, a focus spot with a full-width at half-maximum of 270 nm (= 0.4λ _in ) can be achieved, accompanied by a largely reduced depolarization effect. The sharp waistline indicates that the surface waves are largely converged in the region of focus.     

Does body and fin form affect the maneuverability of fish traversing vertical and horizontal slits?

Synopsis The purpose of this study was to determine if body and fin form affected the maneuverability of teleostean fishes as measured by their ability to negotiate simple obstacles. Obstacles were vertical and horizontal rectangular slits of different widths, for which width was defined as the minimum dimension of a slit irrespective of slit orientation. Performance was measured as the smallest slit width traversed. Three species with different body and fin patterns were induced to swim through slits. Species tested were; goldfish Carassius auratus with a fusiform body, anterio-ventral pectoral fins and posterio-ventral pelvic fins; silver dollars Metynnis hypsauchen with the same fin configurations but a gibbose body; angelfish Pterophyllum scalare with a gibbose body and anterio-lateral pectoral fins. Minimum slit widths negotiated were normalized with the length of various body dimensions: total length, maximum width, span at the pectoral fins, and volume^1/3 (numerically equal to mass^1/3). Goldfish had the poorest performance, requiring the largest slit widths relative to these body dimensions. No consistent patterns in performance were found for silver dollars vs. angelfish. There were no differences among species in the ratio of minimum vertical slit width negotiated to that for horizontal slits, indicating fish were equally able to control posture while swimming on their sides. There were also no consistent patterns in the times taken to transit slits. Although the deep-bodied fish were able to maneuver through smaller slits, the most striking result is the similarity of minimum slit widths traversed in spite of the large variation in body form. Body form and fin plan may be more important for maneuvering and posture control during sub-maximum routine activities.     

A Novel Design Method of Focusing-control Device by Modulating SPPs Scattering

A novel design method of focusing device with a desired focal length is proposed, which consists of a nanometal slit surrounded with the grooves with fixed width and depth. By numerical calculation and analytic derivation, a relation between the phases of the light scattering from slit and grooves and the groove positions is revealed. Under the linear approximation, a design formula of focusing device is deduced, from which the position parameters of the grooves can be easily obtained to modulate the phase of the scattering light. The transmitted field distribution through the illustrative structures designed according to the proposed method is simulated with finite-difference time-domain (FDTD) method. The results show a good agreement with the theoretical analysis, and that the focal length can be controlled in several micrometers distance away from the metal exit surface, which verifies the feasibility of the method to deign focus-controlled optical elements in wavelength scale in integrated optics.     

Plasmonic Lens with Multiple-Turn Spiral Nano-Structures

In this paper, we investigate the focusing properties of a plasmonic lens with multiple-turn spiral nano-structures, and analyze its field enhancement effect based on the phase matching theory and finite-difference time-domain simulation. The simulation result demonstrates that a left-hand spiral plasmonic lens can concentrate an incident right-hand circular polarization light into a focal spot with a high focal depth. The intensity of the focal spot could be controlled by altering the number of turns, the radius and the width of the spiral slot. And the focal spot is smaller and has a higher intensity compared to the incident linearly polarized light. This design can also eliminate the requirement of centering the incident beam to the plasmonic lens, making it possible to be used in plasmonic lens array, optical data storage, detection, and other applications.     

Investigation of Physical Limits of Plasmonic Focusing Lens in Different Regions

We present theoretical studies of three regions for plasmonic focusing, which are surface plasmon-dominating, Fresnel, and Fraunhoffer regions. The boundaries of the three regions are defined and the physical behaviors of plasmonic lenses in terms of focal length and focus size in these regions are investigated. A plasmonic lens that renders a subdiffraction-limit focus in the Fresnel region is presented and the lens performance with respect to the design parameters is studied by using finite-difference time-domain simulations. This work can serve as a basis for understanding plasmonic-focusing phenomenon and designing plasmonic lenses for various applications.     

Cloning, expression and characterization of human tissue-specific DNA polymerase λ2*

DNA polymerase (POL) λ plays an important role during DNA repair and DNA nonhomologous recom-bination processes. A novel POL λ variant was cloned from a human liver cDNA library and named POL λ2 (GenBank Accession No. AY302442). POL λ2 has 2206 base pairs in length with an open reading frame of 1452 base pairs encoding a 482-amino-acids protein. Bioinformatics analysis reveals that POL λ2 spans 7.9 kb on human chromosome 10q24 and is composed of 8 exons and 7 introns. It has the specific domain of DNA polymerase X family-POL Xc at the C-terminus and BRCT domain at the N-terminus. POL λ2 was localized predominantly in nucleus in transfected L0-2 cells. It was expressed abundantly in liver and testis, weakly in ovary, and undetectably in other tested human tissues. In comparison with the expression ratio between POL λ and POL λ2 in normal liver tissues and hepato-cellular carcinoma (HCC) adjacent tissues, the ratio was aberrant in 80% of those 15 HCC specimens examined due to the up-regulated expression of POL λ. This abnormality might be involved in hepato-carcinogenesis. The recombinant POL λ2 with His-tag was expressed as a soluble active protein in E. coli BL21 (DE3)CONDON Plus and purified by Ni-NTA resin and then desalted by Superdex-75 chro-matography in an FPLC system. The analysis using isotope α-³²P-dCTP incorporation in vitro showed that the purified recombinant POL λ2 exhibited DNA polymerase activity.