Fabrication and evaluation of a wideband multilayer laminar-type holographic grating for use with a soft-x-ray flat-field spectrograph in the region of 1.7 keV

A multilayer laminar-type holographic grating having an average groove density of 2400 lines/mm is designed and fabricated for use with a soft-x-ray flat-field spectrograph covering the 0.70-0.75 nm region. A varied-line-spaced groove pattern is generated by the use of an aspheric wavefront recording system, and laminar-type grooves are formed by a reactive ion-etching method. Mo/SiO2 multilayers optimized for the emission lines of Hf-M, Si-K, and W-M are deposited on one of the three designated areas on the grating surface in tandem. The measured first-order diffraction efficiencies at the respective centers of the areas are 18%-20%. The flat-field spectrograph equipped with the grating indicates a spectral linewidth of 8-14 eV for the emission spectra generated from electron-impact x-ray sources.     

Tunable dual-band nearly perfect absorption based on a compound metallic grating

Traditional metallic gratings and novel metamaterials are two basic kinds of candidates for perfect absorption. Comparatively speaking, metallic grating is the preferred choice for the same absorption effect because it is structurally simpler and more convenient to fabricate. However, to date, most of the perfect absorption effects achieved based on metamaterials are also available using an metallic grating except the tunable dual(multi)-band perfect absorption. To fill this gap, in this paper, by adding subgrooves on the rear surface as well as inside the grating slits to a free-standing metallic grating, tunable dual-band perfect absorption is also obtained for the first time. The grooves inside the slits is to tune the frequency of the Cavity Mode(CM) resonance which enhances the transmission and suppresses the reflectance simultaneously. The grooves on the rear surface give rise to the phase resonance which not only suppresses the transmission but also reinforces the reflectance depression effect. Thus, when the phase resonance and the frequency tunable CM resonance occur together, transmission and reflection can be suppressed simultaneously, dual-band nearly perfect absorption with tunable frequencies is obtained. To our knowledge, this perfect absorption phenomenon is achieved for the first time in a designed metallic grating structure.     

The effect of fluctuations in the lateral period of a multilayer grating on the scattering of hard synchrotron radiation

The effect of fluctuations in the lateral period of a nonideal multilayer grating on the scattering of hard synchrotron radiation (X-ray frequency range) was studied. Maps of the angular distribution of the coherent and diffuse scattering intensity in the reciprocal space are constructed. Theoretical diffraction curves calculated for a Ni/C multilayer grating are compared to the experimental data obtained by high-resolution triple-axis diffractometry. It is shown that good agreement between theory and experiment is observed for a fluctuation dispersion within 3% of the average lateral period of the grating.     

Fabrication of three-dimensional polymer quadratic nonlinear grating structures by layer-by-layer direct laser writing technique

We demonstrate the fabrication of a three-dimensional (3D) polymer quadratic nonlinear (χ(2)) grating structure. By performing layer-by-layer direct laser writing (DLW) and spin-coating approaches, desired photobleached grating patterns were embedded in the guest-host dispersed-red-1/poly(methylmethacrylate) (DR1/PMMA) active layers of an active-passive alternative multilayer structure through photobleaching of DR1 molecules. Polyvinyl-alcohol and SU8 thin films were deposited between DR1/PMMA layers serving as a passive layer to separate DR1/PMMA active layers. After applying the corona electric field poling to the multilayer structure, nonbleached DR1 molecules in the active layers formed polar distribution, and a 3D χ(2) grating structure was obtained. The χ(2) grating structures at different DR1/PMMA nonlinear layers were mapped by laser scanning second harmonic (SH) microscopy, and no cross talk was observed between SH images obtained from neighboring nonlinear layers. The layer-by-layer DLW technique is favorable to fabricating hierarchical 3D polymer nonlinear structures for optoelectronic applications with flexible structural design.     

Efficiencies of master, replica, and multilayer gratings for the soft-x-ray-extreme-ultraviolet range: modeling based on the modified integral method and comparisons with measurements

The near-normal-incidence efficiencies of a 2400-groove/mm holographic master grating, a replica grating, and a multilayer grating are modeled in the soft-x-ray-extreme-ultraviolet (EUV) regions and are compared with efficiencies that are measured with synchrotron radiation. The efficiencies are calculated by the computer program PCGrate, which is based on a rigorous modified integral method. The theory of our integral method is described both for monolayer and multilayer gratings designated for the soft-x-ray-EUV-wavelength range. The calculations account for the groove profile as determined from atomic force microscopy with a depth scaling in the case of the multilayer grating and an average random microroughness (0.7 nm) for the short wavelengths. The refractive indices of the grating substrate and coatings have been taken from different sources because of the wide range of the wavelengths (4.5-50 nm). The measured peak absolute efficiency of 10.4% in the second diffraction order at a wavelength of 11.4 nm is achieved for the multilayer grating and is in good agreement with a computed value of approximately 11.5%. Rigorous modeling of the efficiencies of three similar gratings is in good overall agreement with the measured efficiency over a wide wavelength region. Additional calculations have indicated that relatively high normal incidence efficiency (of at least several percent) and large angular dispersion in the higher orders can be achieved in the 4.5-10.5-nm range by application of various multilayer coatings.     

Numerical investigation of a grating and graphene-based multilayer surface plasmon resonance biosensor

A multilayer surface plasmon resonance biosensor (SPRB) incorporating a grating-graphene configuration is investigated for enhanced sensitivity. The numerical analysis of the impact of integrating a periodic array of subwavelength grating on top of a layer of graphene sheet for improving sensitivity is presented. The result of monitoring the biomolecular interactions of DNA hybridization is compared against the outcome of the conventional SPRB, a graphene-based multilayer SPRB, and a multilayer layer grating SPRB, and is mathematically validated. It is demonstrated that the inclusion of a grating and graphene layer on top of the gold thin film is an excellent candidate for a highly sensitive SPRB. To achieve further enhancement of sensitivity, the subwavelength grating is numerically optimized against its geometry including grating configurations (rectangular, sinusoidal, and triangular), grating depth, volume factor, and grating period.     

Quantitative determination of higher harmonic content in the soft x-ray spectra of toroidal grating monochromator using a reflection multilayer

Use of a grating monochromator causes a problem of higher harmonic contaminations in a synchrotron beamline operating in the soft x ray/vacuum ultraviolet region. Generally gratings are used to experimentally determine the higher harmonic contaminations. In this method, the relative contribution of contaminant wavelengths is measured with respect to the first harmonic wavelength (desired wavelength). The quantitative fit of grating spectra is rather complex, and therefore qualitative analysis is carried out. Analysis of multilayer reflectivity data has become rather simple with recent advances in the theoretical modeling. Therefore we propose to use a multilayer mirror and analyze its reflectivity data for quantitative determination of harmonic contamination in a soft x ray beamline. In the present study we used a Mo/Si multilayer of d=97 ? to quantify the spectral purity of 600 lines/mm toroidal grating at the reflectivity beamline of Indus-1 450 MeV synchrotron source. The measured reflectivity spectra at each wavelength is analyzed and the actual contribution of higher harmonics in the incident beam is obtained. Details of methodology and results are discussed.     

Analysis and design of a concave diffraction grating with total-internal-reflection facets by a hybrid diffraction method

A novel hybrid diffraction method is introduced to simulate the diffraction and imaging of a planar-integrated concave grating that has total internal reflection (TIR) facets. The Kirchhoff-Huygens diffraction formula is adopted to simulate the propagation of the lightwave field in the free-propagation region, and a rigorous coupled-wave analysis is used to calculate the polarization-dependent diffraction by the grating. The hybrid diffraction method can be used to analyze accurately the imaging properties as well as the polarization-dependent diffraction characteristics of a concave grating. The dependence of several merit parameters of a concave grating with TIR facets on its basic geometric parameters is studied. Compared with one with metallic echelle facets, a concave grating with TIR facets shows a much lower polarization-dependent loss. Since more performance specifications can be considered in the design of a concave grating than with the conventional scalar method, design error can be reduced greatly with the present hybrid diffraction method.     

Efficiency and long-term stability of a multilayer-coated, ion-etched blazed holographic grating in the 125-133-Å wavelength region

The efficiency of an ion-etched blazed holographic grating was measured by the use of synchrotron radiation in the 125-133-? wavelength range and at near-normal incidence. The grating had a Mo-Si multilayer interference coating that resulted in a peak normal-incidence efficiency of 13% in the second grating order and at a wavelength of 128 ?. This is the highest efficiency obtained to date from a multilayer-coated grating in this wavelength region and at normal incidence. These measurements are compared with similar measurements performed on the same grating 4.5 years later. Over this time the peak grating efficiency decreased from 13% to 8%, and this result is attributed to the decrease in the reflectance of the multilayer coating from 55% to 42%. Oxidation and contamination of the multilayer with carbon appear to be the causes of these losses. The groove efficiency of the grating substrate in the second order is 23%.     

Diffraction Grating EfficienciesConformal Mapping Method for a Good Real Conductor

The metallic diffraction grating problem has been solved for P-polarization using a conformal mapping and the surface impedance boundary condition. The method is used to calculate the electromagnetic fields diffracted by a grating having a cycloidal groove shape. The numerical results are compared with those obtained using the direct differential formalism. For low conductivities the coincidence between both results is only qualitative, whereas there exists a zone for greater conductivities where the differences are smaller than 0·;005. For even greater conductivities the approximated boundary condition employed holds more exactly, but the comparison is not possible because the direct differential method involves numerical problems.     

Optical grating diffraction method: from strain microscope to strain gauge

The grating diffraction method for direct strain measurement is reviewed. Two systems which use this method are presented. The first system is a compact strain microscope. A Leitz optical transmitting microscope with white light source is reconstructed by developing a loading and recording system. Gratings with median density of between 40 and 200 lines/mm are used. With the help of a Bertrand lens, the Fourier spectrum of the grating is formed with high image quality on the CCD sensor plane. Software is developed to precisely, quickly and automatically determine the diffraction spot centroids. The second system is a new strain sensor based on a high-frequency grating and two Position Sensor Detectors (PSDs). The grating, attached to the surface of the specimen, is illuminated by a focused laser beam, generally with a frequency of 1,200 lines/mm. The centroids of diffracted beam spots from the grating are automatically determined using two PSD sensors connected to a personal computer. The shift of diffracted beam spots due to specimen deformation is detected. Strain sensitivity of one micro-strain can be obtained, as can a 0.4 mm spatial resolution for strain measurement. The system can be used for both static and dynamic tests.     

三层亚波长光栅结构的透射特性

设计了一种具有三层结构的亚波长金属光栅,采用时域有限差分（FDTD）法对所设计的三层光栅结构进行仿真计算．与单层金属光栅相比,这种三层的光栅结构具有更好的滤波效果,其透射光谱中峰值可达77％,且能很好地抑制高波段的透射率．分析了各几何参数对所设计的光栅结构透射特性的影响,尤其是对透射光谱中0值位置的影响．结果表明0值位置主要受光栅缝宽、介质层高度和介质折射率的影响,而与金属层光栅的高度无关．其影响规律为偏振滤波器的设计提供了参考．     

Analysis of the polarization-dependent diffraction from a metallic grating by use of a three-dimensional combined vectorial method

A three-dimensional combined vectorial method, which is based on the finite-difference time-domain algorithm and vectorial diffraction formulation, is introduced to analyze the interaction of a realistic focused beam with a metallic grating in an optical storage system. The diffracted field patterns and the detected signals are calculated for gratings with different geometries, and the polarization-dependent characteristics are studied. The combined method can give accurately the detected signals and the field pattern at any desired position of the optical storage system.     

Mo/Si multilayer-coated ruled blazed gratings for the soft-x-ray region

Two Mo/Si multilayer-coated blazed gratings have been fabricated for operation at soft-x-ray wavelengths above the Si L edge, λ ≥ 12.4 nm, at (near) normal incidence. The sawtooth profile of the grating structure was mechanically ruled into a 200-nm Au film that was deposited onto a plane glass substrate. To smooth the rough Au surface and to prevent interdiffusion of the Au film with the upper Mo/Si multilayer, a carbon film was evaporated onto the Au grating surface of one of the gratings before the deposition of the multilayer coating. We matched the multilayer grating, working on blaze in the third diffraction order, in which an absolute diffraction efficiency of 3.4% at a wavelength of 14 nm was measured, whereas only 1.1% was achieved for a similar grating (without a carbon interlayer). These efficiencies are higher than those obtained for other ruled blazed gratings reported in the literature. As a result of the multilayer and grating periodicity, the wavelength of diffraction can be tuned bya rotation of the grating, which is important for application in a soft-x-ray monochromator.     

Metallic film optimization in a surface plasmon resonance biosensor by the extended Rouard method

The extended Rouard method is applied to the computation of a multi-absorbing-layer system for the optimization of surface plasmon resonance (SPR) sensors. Specifically, the effect of the properties of a metallic layer on the shape of the reflectivity and sensitivity curve is demonstrated in the case of a Kretschmann configuration. This theoretical investigation allows us to establish the best optical properties of the metal to obtain a localized SPR, given the illuminating beam properties. Toward the development of a sensitive biosensor based on SPR, we quantify the changes in reflectivity of such an optical biosensor induced by the deposition of a nanometric biochemical film as a function of the metal film characteristics and the illumination operating conditions. The sensitivity of the system emphasizes the potential of such biophotonic technology using metallic multilayer configurations, especially with envisioned metamaterials.     

Tracking control of a multilayer piezoelectric actuator using a fiber bragg grating displacement sensor system

This paper provides a fiber Bragg grating (FBG) sensor system which can measure the point-wise, out-of-plane displacement to examine the position-tracking control problem of a multilayer piezoelectric actuator (MPA). An FBG filter-based wavelength-optical intensity modulation technique is used in this study. A nominal system model is identified experimentally from the responses excited by random signals measured by an FBG displacement sensor that are simultaneously compared with those obtained from a laser Doppler vibrometer. To further investigate the sensing ability of the proposed system in a feedback control problem, control strategies including robust Hα control, proportional-integralderivative control, and pseudoderivative feedback control are implemented. The characteristics of the step responses for each controller are examined. The experimental results show that the proposed sensor system is capable of performing the system identification and can serve as a feedback control sensor which has a displacement sensitivity of 5 mV/nm.     

Normal-incidence efficiencies in the 115-340-Å wavelength region of replicas of the Skylab 3600-line/mm grating with multilayer and gold coatings

Multilayer and gold coatings were applied to replicas of the 3600-line/mm ruled grating that was developed for the Naval Research Laboratory S082A spectroheliograph that was flown on the Skylab spacecraft. The Mo-Si multilayer coating had a peak normal-incidence reflectance of 50% at a wavelength of 136 ?. The normal-incidence efficiency of the multilayer-coated grating was measured by the use of synchrotron radiation and was compared with the efficiency of the gold-coated replica grating in the 115-340-? wavelength region. The peak efficiency of the multilayer grating was 1.3% in the 133-137-? region and was a factor of 65 higher than the efficiency of the gold grating. The multilayer and gold coated gratings, as well as an uncoated replica grating substrate, were characterized by the use of a scanning probe microscope. The rms microroughness of the uncoated and multilayer-coated gratings was 10 ?, and the microroughness of the gold grating was 16 ?.     

Grating-coupled surface plasmon polaritons and waveguide modes in a silver-dielectric-silver structure

A silver-dielectric-silver structure that supports both waveguide modes and surface plasmon polaritons is explored. The upper interface between the dielectric and the silver is periodically corrugated to allow coupling of visible photons to both types of mode. Such a metallic microcavity leads to plasmonic and waveguide self-interacting bandgaps at Brillouin zone boundaries. In addition there are found other bandgaps from mode crossings within the Brillouin zone. This results specifically in a very flat photonic band due to anticrossings between a surface plasmon polariton and waveguide modes. Characterization of the observed modes in terms of their resonant electromagnetic fields is achieved by using a multilayer, multishape differential grating theory.     

Multifunctional lipid multilayer stamping

Nanostructured lipid multilayers on surfaces are a promising biofunctional nanomaterial. For example, surface-supported lipid multilayer diffraction gratings with optical properties that depend on the microscale spacing of the grating lines and the nanometer thickness of the lipid multilayers have been fabricated previously by dip-pen nanolithography (DPN), with immediate applications as label-free biosensors. The innate biocompatibility of such gratings makes them promising as biological sensor elements, model cellular systems, and construction materials for nanotechnology. Here a method is described that combines the lateral patterning capabilities and scalability of microcontact printing with the topographical control of nanoimprint lithography and the multimaterial integration aspects of dip-pen nanolithography in order to create nanostructured lipid multilayer arrays. This approach is denoted multilayer stamping. The distinguishing characteristic of this method is that it allows control of the lipid multilayer thickness, which is a crucial nanoscale dimension that determines the optical properties of lipid multilayer nanostructures. The ability to integrate multiple lipid materials on the same surface is also demonstrated by multi-ink spotting onto a polydimethoxysilane stamp, as well as higher-throughput patterning (on the order of 2 cm(2) s(-1) for grating fabrication) and the ability to pattern lipid materials that could not previously be patterned with high resolution by lipid DPN, for example, the gel-phase phospholipid 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) or the steroid cholesterol.     

Comparison of Metal Parameters Obtained from Prism and Grating Coupling to Surface Plasmon Polaritons

Abstract

Surface plasmon polariton resonances obtained from both prism coupling (in the Otto configuration) and grating coupling to the same metallic surface have been fitted using appropriate theories to give the dielectric constant of the metal at 632·8 nm. Results from silver, aluminium and gold samples have confirmed that the dielectric constants obtained from fitting the data obtained using grating coupling are the same (to within experimental errors) as those obtained from prism-coupled data.

This confirms for the first time the validity of the differential diffraction grating theory by direct comparison with known data for a metallic surface.