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In general, the substrate film is included in a practical Fresnel zone plate (FZP). The dependence of focusing characteristics on the incident direction of light illuminating the binary phase sub-wavelength FZP on substrate film are studied by using the finite-different time-domain method. The simulation results show that, in the range of effective etch depth, the intensity and size of FZP's focusing spot in the far-field region are insensitive to the incident direction. However, the focal length for the light illuminating from the etched structure side of the FZP is larger than that from the substrate film side of the FZP. For these two different incident directions, focal length decreases as the increase of etch depth. And for some special value of etch depth, for example, when the value equals to 700 nm, the depth of focus is quite great in the situation of light illuminating from the etched structure side and the reduction of focusing intensity and resolution of spot is within an acceptable range. The simulation results in this paper are useful for the FZP's applications in microscopy and photolithography.

In previous paper, “Multi-objective optimization of Passive Shock Absorber for Landing Gear”, several new construction of metering pin in passive shock absorber have been proposed, and obtained optimum solutions of metering pin dimensions by multi-objective optimization. The aim of the previous paper is to solve the mass variation problem. The shock absorbers with the results of multi-objective optimization for the new metering pin constructions can be called a “semi semi-active shock absorber”. In this paper, we do single-objective optimization just for simple passive shock absorbers, namely optimization at maximum or minimum masses. The aim of this paper is to evaluate the performance of simple passive shock absorbers with new construction metering pin, not as a semi semi-active shock absorber to deal with the mass variation problem. We proposed single-objective optimization method of passive shock absorber without metering pin, with single and multi-tapered metering pins, and with single and multi-parabolic metering pins. Each of these metering pin constructions have been obtained optimal solutions. Using the optimum solutions, we evaluate and compare the performance of each passive shock absorber without and with different metering pins for maximum or minimum masses. The optimization results and method are helpful in the design of landing gears for various aircrafts, especially, for design of lighter aircraft landing gears, not necessary to be considered mass vibration problem.

The resonance absorption of a multilayered bi-grating which consists of thin-film corrugated periodically in two directions is investigated. The absorption in a multilayered thin-film bi-grating has been of considerable interest since we can expect more complex behaviors in the absorption phenomen by virtue of the presence of double periodicity and multilayer structure. In solving the problem, we employed a computational technique based on modal expansion. Taking a sandwiched structure /Ag/SiO2/Ag/ for an example, we observed: 1) excitation of a single-interface surface plasmon mode at the lit surface of the 1st Ag layer with strong field enhancement for thick enough Ag layer case; 2) excitation of coupled short-range or long-range surface plasmon modes at each surface between vacuum and Ag layers with strong field enhancements for thin enough Ag layer cases no matter with the thickness of SiO2 layers; 3) enhancements of field at surfaces between Ag and SiO2 layers in some cases related with the thickness of SiO2 layers. The coupled plasmon modes were resulted by the resonance waves on four surfaces in these cases.

Backgroud Chinese Luzhou-flavor baijiu (LFB) was fermented in an underground cellar, and the bottom and side of the cellar were covered with pit muds (PMs), where the metabolic activity of the microorganisms had a significant effect on the LFB quality. PMs can be divided into aged pit mud (AP) and degenerated pit mud (DP), thus, the qualities of LFB generated from AP and DP were different. In this essay, metatranscriptomics method was applied to illustrate the differences of the two PMs, as well as to search out the pivotal microorganisms and genes influencing the quality of LFB. Results Archaea, Clostridium and some thermophilic microorganisms might bring significant effect in AP, while the active eukaryota and Anaeromyxobacter would cause degeneration in PM. Also, the metabolism of carbohydrate and amino acid were more active in AP. What is more, carbohydrate, amino acid and their derivant can produce important organic acids via the activity of the microorganisms in PMs. There were eight critical enzymes noticed in the organic acids metabolic pathway, which were more actively expressed in AP, demonstrating active expression of the critical genes related to organic acid metabolism could have a positive effect on LFB quality. Conclusion This study identified specific differences in active microorganisms, active expressed genes and the expression levels of key genes in vital metabolic pathway between AP and DP. Which may be the actual reason for the differences in the quality of LFB made from different PMs. Mastering these results will provide assistance to improve the quality of LFB. © 2021 Society of Chemical Industry.

With the increasing popularity of soy sauce containing high amounts of amino acid nitrogen (AAN) in China and the positive correlation of biogenic amines (BAs) with AAN, reducing BAs formation during soy sauce fermentation has become an urgent task. In this work, the effect of salt-tolerant yeasts and Staphylococcus piscifermentans on BAs formation was extensively studied. Combined inoculation for different osmotolerant yeast strains indicated that Z. rouxii CICC 1417 and T. candida CICC 1019 co-inoculation produced the lowest amount of BAs (89.43 mg/L). Furthermore, co-inoculation of soy sauce mash with S. piscifermentans and salt-tolerant yeasts reduced the BAs production by 31.51% under laboratory-scale experiments. Only 133.40 g/L BAs were produced after S. piscifermentans inoculation in 50-T fermentator, and this value was 63.25% lower than that of the control. Most of the alcohols, aldehydes, phenols, and esters were increased, whereas bacteria, such as Pediococcus, Weissella, and Streptococcus, were inhibited and thus reduced BAs formation. The increased abundance in Zygosaccharomyces and Pichia may contribute to the improvement in volatile compound production. These findings reveal the high potential of the co-inoculation of S. piscifermentans and salt-tolerant yeasts for soy sauce production with limited BAs formation.

Derived from RNA, 5'-ribonucleotides, especially Inosine-5'-monophosphate (IMP) and guanosine-5'-monophosphate (GMP), can enhance the umami taste of soy sauce. In this study, the RNA content of three different salt-tolerant yeasts was examined. The most valuable strain was subjected to atmospheric and room-temperature plasma (ARTP) mutagenesis, which improved its RNA content by 160.54%. Regular fermentation with RNA-enhanced strain failed to increase the amount of 5'-ribonucleotides in the soy sauce due to hydrolysis by phosphatase. A two-stage fermentation strategy was then carried out. Aroma compounds were mainly synthesized in the first stage, and RNA-enriched biomass was massively produced in the second stage followed by heat treatment to inactivate phosphatase. After the proposed strategy was applied, IMP and GMP in the soy sauce reached 68.54 and 89.37 mg/L, respectively. Moreover, the amounts of key aroma compounds and organic acids significantly increased. Results may provide new insights for improving the quality of soy sauce through microorganism breeding and fermentation control.

Numerical solution is presented for light scattering from two kinds of free-standing periodic arrays, that is, disks made of noble-metal and circular apertures perforated in a thin noble-metal sheet. The shapes of them are complementary to each other, and the circular areas are allocated along two orthogonal coordinates with the same periodicity. Using the generalized boundary conditions of the surface impedance type, we formulate the boundary value problem into a set of integral equations for unknown electric and magnetic current densities defined over the circular area. Employment of the method of moments allows us to solve the integral equations and give the expansion coefficients of the current densities, from which we can find reflected, transmitted, and absorbed powers. Dependence of the powers on the array parameters and wavelength is discussed in detail from the viewpoint of grating resonance. Special attention is paid to the extraordinary transmission which occurs in the arrays of apertures of sub-wavelength size by analytical derivation of the quasi-static solutions.

Based on the scattering theory and the Green function method, a dynamical theory is given for calculating the difiraction of deeply-etched gratings with a stratifled structure substrate. The key of our method is that the patterned grating structure is considered as a perturbation to the unpatterned stratifled structure rather than to vacuum. Using the flrst-order Born approximation and in the Fresnel difiraction region, we obtain a simple analytical expression, which can be used to calculating the scattering intensity of deeply-etched circular binary Fresnel zone plates with a stratifled substrate (MDECBFZPs). The numerical results show that the focusing intensity at the foci of the MDCBFZP changes periodically with the etching depth and the thickness of the substrate fllm. Our results are in good agreement with FDTD simulations.

The optical trapping characteristics of highly focused higher-order radially polarized beams (R-TEM p1 *) acting on a Rayleigh particle are studied theoretically. Numerical results show that as the order p of beam increases and the numerical aperture NA o of the objective decreases, the axial trap distance increases but the trap depth and maximum restoring force decreases. In a limit of NA o = 1, three higher-order R-TEM p1 * beams of p = 1, 2, 3, like the fundamental lowest-order radially polarized beam of p = 0, can three-dimensionally trap a particle to the focus but the axial trap stiffness decreases with the increase of p . When NA o = 0.95, the focus is still a stable trap point for the two beams of p = 0 and 1 but it becomes an unstable trap point for the two beams of p = 2 and 3. The trap stability is also discussed for higher-order radially polarized beam illumination.

We present an idea of grating-based plasmon biosensor utilizing phase detection to realize high resolution in flnding a refractive index of a material put on the surface of a metal grating. Considering a trade-ofi between high resolution and experimental practicability, we show a table of recommended setup that covers a wide range of the index. Keeping the difiraction e-ciency no less than 10 i3 and assuming the resolution in phase detection to be 2:5 £ 10 i2 degrees, we estimate the resolution of the biosensor as 7:5£10 i7 refractive index units. We also discuss the possible improvement to realize a predicted superior limit of resolution around 10 i8 refractive index units.

We theoretically report a method of the near-field double-spot subwavelength-photolithography by attaching an optical anisotropic metamaterial (OAM) and polymer composite film to a solid immersion lens (SIL). The OAM made up of metallic nanowires embedded in a dielectric matrix can realize all-angle negative refraction for TM waves in the visible regime. When the SIL near-field photolithography system with a nanoscale OAM–polymer composite film is illuminated by a linearly-polarized beam, the longitudinal component of electric field in the focal region of the objective is largely enhanced by surface plasmons and the transverse component is suppressed. Consequently, a spot in the conventional near-field photolithography system with a bare SIL is split into two spots with subwavelength spacing. If the present focusing system with an OAM–polymer film is used to near-field photolithography, a subwavelength-spacing (wavelength/5) and deep photoetching pattern can be achieved and, compared with the conventional single-spot photolithography, the photoetching speed can be doubled.

We numerically analyze surface plasmon resonance absorption of incident light en- ergy by a multilayered bigrating, which consists of dielectric and metallic thin-fllms corrugated periodically in two directions. We apply Yasuura's modal expansion method for solving the prob- lem of plane-wave difiraction by a multilayered bigrating and evaluating the absorption, which is observed as dips in difiraction e-ciency curves. Employing the numerical algorithm, we numer- ically examine characteristics of the surface plasmon resonance absorption in the multilayered bigrating.

We numerically analyze surface plasmon resonance absorption of incident light energy by a multilayered grating, which consists of a stack of periodically corrugated metal and dielectric films. We apply Yasuura's modal expansion method for solving the problem of plane-wave diffraction by a multilayered grating. Employing the numerical algorithm, we evaluate the resonance absorption which is observed as dips of diffraction efficiency curves. We investigate field distributions in the vicinity of a multilayered grating when the absorption occurs. We thus show that the surface plasmons are excited on a thin metal film embedded in a multilayered grating. In view of the design of a multilayered thin-film grating, we investigate the influence of the corrugation depth and the refractive index of a substrate on characteristics of plasmon resonance absorption.

An effective computational method based on a conven- tional modal expansion approach is presented for handling a multilay- ered dielectric grating whose profiles are multilayered and sinusoidally modulated. This structure fabricated by dielectric material is one of the useful photonic crystals. The method is based on Yasuura's modal expansion, which is known as a least-squares boundary residual method or a modified Rayleigh method. In the extended method, each layer is divided into shallow horizontal layers. The Floquet modal func- tions and approximate solutions are defined in each shallow layer, and the latter are matched with boundary conditions in the least-squares sense. A huge-sized least-squares problem that appears in finding the modal coefficients is solved by the QR decomposition accompanied by sequential accumulation. This procedure makes it possible to treat the case where the groove depths are the same as or a little more than the grating period. As numerical example, we calculate a diffractive char- acteristic by a multilayered deep dielectric grating and confirm that a common band gap occurs for both polarizations.

Excitation of plasmons on the surface of a metal grating placed in planar or conical mounting is investigated in detail. Most of the results of numerical computations are compared with experimental data. When a TM wave illuminates a metal grating, total or partial absorption of incident light occurs at angles of incidence at which the plasmon surface waves are excited. In planar mounting the absorption is generally strong and nearly total absorption is observed. While in conical mounting, it is not so strong as that in the planar mounting case and a considerable amount of incident power is reflected. This, however, is accompanied by enhanced TM-TE mode conversion and the greater part of the reflected wave is in the TE polarization. The reciprocal of the TM-wave efficiency, hence, is a practical measure in finding the angles of incidence at which the plasmons are excited. Because the angles are sensitive functions of the refractive index of a material over the grating surface, this phenomenon can be used as an index sensor.

Yasuura's mode-matching method is employed in the investigation of plasmon resonance-absorption in a metal grating with a gold over-coating and the results are compared with experimental data. Enhancement of TM-TE mode conversion accompanying the plasmon resonance-absorption is examined. When a TM wave is incident on a metal grating, enhanced TM-TE mode conversion occurs at angles of incidence at which the surface plasmons are excited. The strength of the mode conversion depends strongly on the azimuth angle of the mounting. This is verified by experiment and an application for refractive-index measurement is suggested.

The authors numerically investigated the characteristics of surface plasmons excited on a thin metal grating placed in planer or conical mounting. After formulating the problem, the solution method, Yasuura’s method (a modal expansion approach with least-squares boundary matching) was described. Although the grating is periodic in one direction, coupling between TE and TM waves occurs because arbitrary incidence is assumed. This requires the employment of both TE and TM vector modal functions in the analysis. Numerical computations showed: (1) the excitation of surface plasmons with total or partial absorption of incident light; (2) the resonance character of the coefficient of an evanescent order that couples the plasmon surface wave; (3) the field profile and Poynting’s vector. The plasmons excited on the surfaces of a thin metal grating are classified into three types: SISP, SRSP, and LRSP, different from each other in the feature of field profile and energy flow. In addition, the eigenvalue of a plasmon mode was obtained by solving a sequence of diffraction problems with complex-valued angles of incidence and using the quasi-Newton algorithm to predict the real angle of incidence at which the absorption occurs.

An effective computational method based on a conven- tional modal-expansion approach is presented for solving the problem of diffraction by a deep grating. The groove depth can be the same as or a little more than the grating period. The material can be a perfect conductor, a dielectric, or a metal. The method is based on Yasuura's modal expansion, which is known as a least-squares boundary residual method or a modified Rayleigh method. The feature of the present method is that: (1) The semi-infinite region U over the grating sur- face is divided into an upper half plane U0 and a groove region UG by a fictitious boundary (a horizontal line); (2) The latter is further di- vided into shallow horizontal layers U1 ,U 2, ··· ,U Q again by fictitious boundaries; (3) An approximate solution in U0 is defined in a usual manner, i.e., a finite summation of up-going Floquet modal functions with unknown coefficients, while the solutions in Uq (q =1 , 2, ··· ,Q ) include not only the up-going but also the down-going modal functions; (4) If the grating is made of a dielectric or a metal, the semi-infinite region L below the surface is partitioned similarly into L0 ,L 1, ··· ,L Q, and approximate solutions are defined in each region; (5) A huge-sized least squares problem that appears in finding the modal coefficients is solved by the QR decomposition accompanied by sequential accu- mulation. The method of solution for a grating made of a perfect conductor is described in the text. The method for dielectric gratings can be found in an appendix. Numerical examples include the results for perfectly conducting and dielectric gratings.

We investigate resonance absorption of incident light energy in a multilayered grating, which is a stack of metal and dielectric films periodically corrugated in one direction. The absorption is associated with two kinds of resonant scattering in a multilayered structure: excitation of coupled surface plasmons on a thin metal film and resonance of electromagnetic fields in a dielectric film (or slab) embedded in a thin metal film. Results of numerical computation confirm the presence of the resonant scattering and show interesting behaviors in the absorption phenomenon.

Fluorescent labeling is the prevailing imaging technique in cell biological research. When statistical investigations on a large number of cells are involved, experimental study is required for both low magnification to get a reliable statistical population and high contrast to achieve accurate diagnosis on the nature of the cells’ perturbation. As microscope objectives of low magnification generally yield low collection efficiency, such studies are limited by the fluorescence signal weakness. To overcome this technological insufficiency, Le Moal et al. proposed a method based on metal-coated substrates that enhanced the fluorescence process and improved collection efficiency in fluorescence microscope observation and that could be directly used with a common microscope setup. In this paper, we use an Ag-Si3N4-Ag multilayer film coated on the substrate and numerically analyse the optical behavior of a fluorophore which was placed above the composited film coated on the substrate. The results shows that by using an Ag-Si3N4-Ag composited film the fluorescence imaging can be enhanced remarkably.

Metal gratings have an interesting property known as resonance absorption in the optics region [Raeter 1982], which causes partial or total absorption of incident light energy. This absorption is associated with the resonant excitation of plasmons on a grating surface; incident light couples with surface plasmons via an evanescent spectral order generated by the grating [Nevier 1982]. Resonance absorption in metal film gratings has been the subject of many theoretical [Nevier 1982] and experimental investigations focused on various applications including chemical sensing [DeGrandpre 1990, Zoran 2009], surface enhanced phenomena such as Raman scattering [Nemetz 1994], and photonic bandgaps [Barnes 1995, Tan 1998].

A grating-based biosensor via phase detection is stated. The resolution will be 10-7 RIU in the state-of-the-art today. The workspace can be shifted in a large range while the sensor resolution can remain in a high level by only changing the incident angle.

An optical-trap method based on the illumination of a double-ring-shaped radially polarized beam (R-TEM${}_{11}^{*}$) is proposed. The numerical results based on the vector diffraction theory show that a highly focused R-TEM${}_{11}^{*}$ beam not only can produce a bright spot but also can form an optical cage in the focal region by changing the truncation parameter $\ensuremath{\beta}$, defined as the ratio of the radius of the aperture to the waist of the beam. The radiation forces acting on Rayleigh particles are calculated by using the Rayleigh scattering theory. The bright spot generated by the R-TEM${}_{11}^{*}$ beam with a $\ensuremath{\beta}$ value close to 2 can three-dimensionally trap a particle with a refractive index larger than that of the ambient. An optical cage or three-dimensional dark spot generated by the R-TEM${}_{11}^{*}$ beam with a $\ensuremath{\beta}$ value close to 1.3 can three-dimensionally trap a particle with refractive index smaller than that of the ambient. Because the adjustment of the truncation parameter can be actualized by simply changing the radius of a circular aperture inserted in the front of the lens, only one optical-trap system in the present method can be used to three-dimensionally trap two types of particles with different refractive indices.

Sensing applications on refractive index based on metal gratings are investigated. The excitation of surface plasmon on a metal grating placed in planer or conical mounting is examined. Numerical results are compared with experimental data. When a TM wave illuminates a metal grating, total or partial absorption of incident light occurs at angles of incidence at which the surface plasmon waves are excited. A conical mounting is introduced in the sensing application in which an enhancement of TM-TE mode conversion is observed in close vicinity to the resonance angle at which almost of the reflected light is in TE polarization. This, hence, makes the reciprocal of the TM-wave efficiency a good measure in finding the angles of incidence at which the surface waves are excited, which leads to a precise measurement. Yasuura's modal-expansion method is introduced in the numerical simulation. The setup for sensing application is represented in details.