Conical Mounting Research Articles

Coupled-mode theory and Fano resonances in guided-mode resonant gratings: the conical diffraction mounting.

We study resonances of guided-mode resonant gratings in conical mounting. By developing 2D time-dependent coupled-mode theory we obtain simple approximations of the transmission and reflection coefficients. Being functions of the incident light's frequency and in-plane wave vector components, the obtained approximations can be considered as multi-variable generalizations of the Fano line shape. We show that the approximations are in good agreement with the rigorously calculated transmission and reflection spectra. We use the developed theory to investigate angular tolerances of the considered structures and to obtain mode excitation conditions. In particular, we obtain the cross-polarization mode excitation conditions in the case of conical mounting.

Wide wavelength range tunable one-dimensional silicon nitride nano-grating guided mode resonance filter based on azimuthal rotation

We describe wavelength tuning in a one dimensional (1D) silicon nitride nano-grating guided mode resonance (GMR) structure under conical mounting configuration of the device. When the GMR structure is rotated about the axis perpendicular to the surface of the device (azimuthal rotation) for light incident at oblique angles, the conditions for resonance are different than for conventional GMR structures under classical mounting. These resonance conditions enable tuning of the GMR peak position over a wide range of wavelengths. We experimental demonstrate tuning over a range of 375 nm between 500 nm˜875 nm. We present a theoretical model to explain the resonance conditions observed in our experiments and predict the peak positions with show excellent agreement with experiments. Our method for tuning wavelengths is simpler and more efficient than conventional procedures that employ variations in the design parameters of structures or conical mounting of two-dimensional (2D) GMR structures and enables a single 1D GMR device to function as a high efficiency wavelength filter over a wide range of wavelengths. We expect tunable filters based on this technique to be applicable in a wide range of fields including astronomy and biomedical imaging.

Numerical method of applying shadow theory to all regions of multilayered dielectric gratings in conical mounting.

Nakayama's shadow theory first discussed the diffraction by a perfectly conducting grating in a planar mounting. In the theory, a new formulation by use of a scattering factor was proposed. This paper focuses on the middle regions of a multilayered dielectric grating placed in conical mounting. Applying the shadow theory to the matrix eigenvalues method, we compose new transformation and improved propagation matrices of the shadow theory for conical mounting. Using these matrices and scattering factors, being the basic quantity of diffraction amplitudes, we formulate a new description of three-dimensional scattering fields which is available even for cases where the eigenvalues are degenerate in any region. Some numerical examples are given for cases where the eigenvalues are degenerate in the middle regions.

Investigating the effect of low dose ionising radiation on epithelial progenitor cell niches

SummaryRecent work has identified a nonlinear biological response to low dose radiation in support of the low dose hormesis model in the murine lens epithelium, with mice being irradiated with doses between 0.1 and 1 Gy, with the dose response peaking at 0.5 Gy (Markiewicz et al., 2015). An important question is whether other epithelia show similar low dose hormetic responses and whether there are any associated pathologies. These comparative studies will help us understand how low dose IR causes cataract. We have developed a conical gel mount system on glass microscopy slides for the mouse lens, which allows its placement and manipulation using a standard inverted confocal microscope. Each lens was subsequently imaged with the Leica SP5 confocal microscope through a set of sequential z stacks, and reconstructed in ImageJ to produce the 3D anaglyphs to measure cell density, cell proliferation and cell apoptosis events in the lens epithelium. By comparison, conventional histochemistry was sufficient to make similar measurements for the progenitor cell niches in the hair follicle and colonic crypts and therefore to determine whether there is a common or distinct hermetic response by the lens epithelium to low dose ionizing radiation.

Polynomial modal analysis of lamellar diffraction gratings in conical mounting.

An efficient numerical modal method for modeling a lamellar grating in conical mounting is presented. Within each region of the grating, the electromagnetic field is expanded onto Legendre polynomials, which allows us to enforce in an exact manner the boundary conditions that determine the eigensolutions. Our code is successfully validated by comparison with results obtained with the analytical modal method.

3-3: Study on the Field of View Properties for a Holographic Waveguide Display System

The Field of View (FOV) properties and effects of the reflection Volume Holographic Grating (VHG) in conical mounting was studied when used in a see through Head Mounted Display in detail. Also, two methods for enlarging the FOV and improving the color uniformity for reflection VHG were analyzed and simulated.

Properties of wideband resonant reflectors under fully conical light incidence.

Applying numerical modeling coupled with experiments, we investigate the properties of wideband resonant reflectors under fully conical light incidence. We show that the wave vectors pertinent to resonant first-order diffraction under fully conical mounting vary less with incident angle than those associated with reflectors in classical mounting. Therefore, as the evanescent diffracted waves drive the leaky modes responsible for the resonance effects, fully-conical mounting imbues reflectors with larger angular tolerance than their classical counterparts. We quantify the angular-spectral performance of representative resonant wideband reflectors in conic and classic mounts by numerical calculations with improved spectra found for fully conic incidence. Moreover, these predictions are verified experimentally for wideband reflectors fashioned in crystalline and amorphous silicon in distinct spectral regions spanning the 1200-1600-nm and 1600-2400-nm spectral bands. These results will be useful in various applications demanding wideband reflectors that are efficient and materially sparse.

Excavation of the approach to the mountain palace-fortress at Herodium

In 2014, the Ehud Netzer Expedition for the Study of Herodium from the Hebrew University commenced excavations in the area of the approach to the mountain palace-fortress at Herodium (hereafter “the mountain palace”). The excavations produced surprising new data with respect to the stages of construction and the layout of the entrance to the hilltop structure, shedding light on Herod's last building project at the site at the time when he transformed the entire hill into his burial and memorial complex (fig. 1 in colour).The presence of a monumental stairway ascending the NE slope of the mount and leading to the structure at its top has long been known, as was that of a sloping passageway that led to the door entering the mountain palace. This arched passageway was intended to make entry possible through the fill of the conical artificial mount. Also prior to the new excavations the entrance room of the hilltop structure was known. The door leading into the courtyard of the palace had been exposed during the Franciscan excavations directed by V. Corbo in the early 1960s, while in 1968-69 G. Foerster exposed the S part of the entrance room, as well as some of the upper arches of the passageway (fig. 2).

Fourier method for modeling slanted lamellar gratings of arbitrary end-surface shapes in conical mounting.

An efficient modal method for numerically modeling slanted lamellar gratings of isotropic dielectric or metallic media in conical mounting is presented. No restrictions are imposed on the slant angle and the length of the lamellae. The end surface of the lamellae can be arbitrary, subject to certain restrictions. An oblique coordinate system that is adapted to the slanted lamella sidewalls allows the most efficient way of representing and manipulating the electromagnetic fields. A translational coordinate system that is based on the oblique Cartesian coordinate system adapts to the end-surface profile of the lamellae, so that the latter can be handled simply and easily. Moreover, two matrix eigenvalue problems of size 2N × 2N, one for each fundamental polarization of the electromagnetic fields in the periodic lamellar structure, where N is the matrix truncation number, are derived to replace the 4N × 4N eigenvalue problem that has been used in the literature. The core idea leading to this success is the polarization decomposition of the electromagnetic fields inside the periodic lamellar region when the fields are expressed in the oblique translational coordinate system.

Propagation of grating-coupled surface plasmon polaritons and cosine–Gauss beam generation

When a surface plasmon polariton (SPP) is excited through a metallic grating in the conical mounting configuration, it propagates along a direction nonparallel to the grating Bragg vector. We will derive, under any possible coupling condition, the propagation direction as a function of experimental parameters, with particular attention to its relation with the azimuthal rotation angle. We will identify the conditions to achieve the maximum angular deflection with respect to the grating vector, also in relation to the grating geometry. Moreover, we will investigate the special configuration in which two SPP modes propagating toward different directions are simultaneously excited by the same light beam, suggesting to exploit this configuration to generate nondiffractive plasmonic beams (cosine–Gauss beams). The analytical treatment is supported by simulations with Chandezon’s method.

Enhancement and control of surface plasmon resonance sensitivity using grating in conical mounting configuration.

In this work we propose a method to enhance and control the angular sensitivity of a grating coupled surface plasmon resonance (GCSPR) sensor. We lighted a silver grating, mounted in conical configuration, with a laser source and we measured the transmittance of the grating as a function of the azimuthal angle. To evaluate the sensitivity, grating surface was functionalized with four different alkanethiol self assembled monolayers (SAM) and the correspondent azimuthal transmittance peak shifts were measured. The sensitivity control was performed by simply change the light incident angle. This method offers the possibility to design dynamic GCSPR sensor benches that can be used to amplify the SPR angle shift at any step of a biological detection process.

Design of dense transmission diffraction gratings for high efficiency.

We propose a design method for dense surface-relief diffraction gratings with high efficiency in transmission mode. Closed-form analytical relations between diffraction efficiency, polarization, and grating parameters are derived and verified in the resonance domain of diffraction under general three-dimensional angles of incidence traditionally termed conical mounting. A powerful tool for rigorous design of computer-generated holograms and diffractive optical elements with spectroscopic scale periods is now enabled.

Mueller matrix ellipsometric detection of profile asymmetry in nanoimprinted grating structures

Mueller matrix ellipsometry (MME) is applied to detect foot-like asymmetry encountered in nanoimprint lithography (NIL) processes. We present both theoretical and experimental results which show that MME has good sensitivity to both the magnitude and direction of asymmetric profiles. The physics behind the use of MME for asymmetry detection is the breaking of electromagnetic reciprocity theorem for the zeroth-order diffraction of asymmetric gratings. We demonstrate that accurate characterization of asymmetric nanoimprinted gratings can be achieved by performing MME measurements in a conical mounting with the plane of incidence parallel to grating lines and meanwhile incorporating depolarization effects into the optical model. The comparison of MME-extracted asymmetric profile with the measurement by cross-sectional scanning electron microscopy also reveals the strong potential of this technique for in-line monitoring NIL processes, where symmetric structures are desired.

Electromagnetic modelization of spherical focusing on a one-dimensional grating thanks to a conical B-spline modal method.

Focusing light onto nanostructures thanks to spherical lenses is a first step in enhancing the field and is widely used in applications. Nonetheless, the electromagnetic response of such nanostructures, which have subwavelength patterns, to a focused beam cannot be described by the simple ray tracing formalism. Here, we present a method for computing the response to a focused beam, based on the B-spline modal method adapted to nanostructures in conical mounting. The eigenmodes are computed in each layer for both polarizations and are then combined for the computation of scattering matrices. The simulation of a Gaussian focused beam is obtained thanks to a truncated decomposition into plane waves computed on a single period, which limits the computation burden.

Erratum to: Coupled SPP Modes on 1D Plasmonic Gratings in Conical Mounting

Erratum to: Coupled SPP Modes on 1D Plasmonic Gratings in Conical Mounting

Analysis of Low Grazing Scattering by Dielectric Gratings in Conical Mounting Using Scattering Factors

Analysis of Low Grazing Scattering by Dielectric Gratings in Conical Mounting Using Scattering Factors

Near-field numerical analysis of surface plasmon polariton propagation on metallic gratings

Purpose – The purpose of this paper is to simulate and analyze the excitation and propagation of surface plasmon polaritons (SPPs) on sinusoidal metallic gratings in conical mounting. Design/methodology/approach – Chandezon's method has been implemented in MATLAB environment in order to compute the optical response of metallic gratings illuminated under azimuthal rotation. The code allows describing the full optical features both in far- and near-field terms, and the performed analyses highlight the fundamental role of incident polarization on SPP excitation in the conical configuration. Findings – Results of far-field polarization conversion and plasmonic near-field computation clearly show that azimuthally rotated metallic gratings can support propagating surface plasmon with generic polarization. Originality/value – The recent papers experimentally demonstrated the benefits in sensitivity and the polarization phenomenology that are originated by an azimuthal rotation of the grating. In this work, numerical simulations confirm these experimental results and complete the analysis with a study of the excited SPP near-field on the metal surface.

Coupled SPP Modes on 1D Plasmonic Gratings in Conical Mounting

Plasmonic nanostructures exhibit a variety of surface plasmon polariton (SPP) modes, with different characteristic properties. While a single metal dielectric interface supports a single-interface SPP mode, a thin metal film can support extended long range SPPs and strongly confined short range SPPs. When the coupling between the incident light and the SPP is provided through a diffraction grating, it is possible to azimuthally rotate the grating with respect to the scattering plane, introducing the possibility to propagate the SPP along an arbitrary direction. We present a theoretical and experimental analysis of the coupling conditions for long range and short range SPPs under this configuration. We also investigate the propagation length of the modes depending on the propagation direction with respect to the grating grooves, showing in particular that the long range SPP propagation length can be sensibly enhanced with respect to the null-azimuth case.

Implementation and testing of a compact and high-resolution sensing device based on grating-coupled surface plasmon resonance with polarization modulation

An experimental setup exploiting grating-coupled surface plasmon resonance (GCSPR) technique based on polarization modulation in conical mounting is presented for the first time. A metallic grating is azimuthally rotated in order to support excitation of surface plasmon polaritons (SPPs) with enhanced sensitivity. In correspondence of SPP resonance, a polarization scan of the incident light is performed and reflectivity is collected. Output signal exhibits harmonic dependence on polarization and the phase term is exploited as a parameter for sensing analysis. Since the sensing configuration is kept fixed during the analysis and the only degree of freedom is represented by the incident polarization, the mechanical complexity of this SPR system is significantly reduced with respect to other configurations. Moreover the setup assures competitive performance in refractive index sensitivity and resolution. The assembled prototype is tested for fluid analysis with an embedded glass/PDMS microfluidic cell fabricated by soft-lithography procedure. A model biorecognition assay based on avidin/biotin reaction was considered in order to test the detection performance of the presented setup.

Polarization separation of light in holographic grating reflection in conical mounting

We experimentally investigate the interaction of linearly polarized light with a holographic grating in a conical mounting. Due to the periodic structure, the polarization properties of the reflected zeroth-order beam are highly sensitive to the conical angle. When a focused Gaussian beam with linear polarization impinges on an air–grating interface at an exceptional conical angle, a spatial splitting of the reflected beam is observed behind a polarizer. We find that it can be interpreted using the anisotropy of the polarization distribution in holographic grating reflection.