Flow characteristics of pressure reducing valve with radial slit structure for low noise

Pressure reducing valves are widely used to maintain the pressure of gas reservoirs to specific values. In a normal valve, supply pressure is decompressed with an orifice structure. When compressed air passes through the orifice structure, considerable noise occurs at the downstream side. In this paper, we have developed a radial slit structure that can reduce pressure without noise. The noise is reduced by changing the orifice structure into the radial slit structure. The radial slit structure valve reduces pressure without noise by suppressing the generation of turbulence and shock wave at the downstream. The analysis of the flow in radial slit structure was achieved by CFD2000 software. The flow rate and pressure distribution were simulated and compared with the experimental result. To confirm the generation of shock wave, the flow of orifice and radial slit structure at the downstream was visualized by Schlieren photography method. A shock wave was generated in the orifice structure, but no shock wave was generated in the radial slit structure. Noise reduction efficiency was investigated by the experiment. The experiment apparatus was set up to JIS standards. The experimental results indicated that the noise level decreased by approximately 40 dB in the slit structure. It is confirmed that the radial slit structure has effectiveness for low noise in the pressure reducing flow. And, it is expected that it can be applied to various kinds of industrial fields.     

Scattering mechanism in a step-modulated subwavelength metal slit: a multi-mode multi-reflection analysis

In this paper, the scattering/transmission inside a step-modulated subwavelength metal slit is investigated in detail. We firstly investigate the scattering in a junction structure by two types of structural changes. The variation of transmission and reflection coefficients depending on structural parameters are analysed. Then a multi-mode multi-reflection model based on ray theory is proposed to illustrate the transmission in the step-modulated slit explicitly. The key parts of this model are the multi-mode excitation and the superposition procedure of the scatterings from all possible modes, which represent the interference and energy transfer occurring at the interfaces. The method we use is an improved modal expansion method (MEM), which is a more practical and efficient version compared with the previous one [C. Li, Y.S. Zhou, H.Y. Wang, F.H. Wang, Opt. Express 19, 10073 (2011)]. In addition, some commonly used methods including FDTD, scattering matrix method and improved characteristic impedance method are compared with MEM to highlight the accuracy of these methods.     

Efficient directional excitation of surface plasmon polaritons by partial dielectric filling slit structure

In this paper, we investigate the excitation of surface plasmon polariton (SPP) in the metallic slit partly filled with dielectric by using the finite-difference time-domain method. It is found that the slit structure displays high asymmetry in the field distribution and SPP excitation due to the difference in matching degree of SPP wavevector on the two sides of slit exit. At certain incident wavelengths, the power flow carried by SPP modes on one side of slit exit is over three orders of magnitude greater than that on the other side, an efficient directional excitation is achieved. The SPP generation efficiencies on both sides of slit exit can be periodically adjusted by the dielectric width, but their changes are not synchronous, implying that such slit structure could be acted as a directional splitter/coupler. Moreover, the asymmetry degree of SPP excitation can also be modulated by the refractive index of dielectric layer.     

Gas molecule-molecule interaction and the gas-surface scattering effect on the rarefied gas flow through a slit into a vacuum

The effect of the gas molecule-molecule interaction and the gas-surface scattering on the gas flow through a slit into a vacuum are investigated in a wide range of the gas rarefaction using the direct simulation Monte Carlo method. To study the gas molecule-molecule interaction influence, we used the variable hard sphere and variable soft sphere models defined for an inverse-power-law potential and the generalized hard sphere model defined for the 12–6 Lennard-Jones potential. The Maxwell, Cercignani-Lampis, and Epstein models were used to simulate the gas-surface scattering. This study demonstrates that the gas molecule-molecule interaction can have a significant influence on the rarefied gas flow through a slit, while the influence of the gas-surface scattering is negligibly small. The presented numerical results are in agreement with the corresponding experimental ones. The article is published in the original.     

Two-dimensional multispecies imaging of a supersonic nozzle flow

Raman imaging is shown to be a very suitable technique for simultaneous density mapping of different species in dry air and N(2) supersonic nozzle flows. The salient features of Raman scattering are its molecular sensitivity and the fact that it can be spectrally separated from strong reflections and Mie scattering. We collected Raman images of both N(2) and O(2) concurrently by imaging the flow through an imaging spectrograph with a broad entrance slit onto a CCD camera. The main advantage of this method is that different species can be imaged under exactly the same flow conditions.     

How diffraction limits ultrasonic screening in phononic plate composed of a periodic array of resonant slits

We explore experimentally the role played by diffraction in the phenomenon of acoustic shielding provided by a plate that is periodically perforated with subwavelength slits and immersed in water. We carried out ultrasonic transmission measurements for all directions of propagation in order to check the omnidirectionality of acoustic shielding. While a single slit acts as a Fabry–Perot resonator in the frequency range of interest, the coupling between adjacent slits provides an attenuation frequency band centered around the resonant frequency that is mostly independent of the angle of incidence. Beyond the incident angle of 45 degrees, however, we observe the appearance of scattered radiation that limits the attenuation of ultrasound. This spurious scattering is shown to arise from diffraction by the grating of slits.     

Plasmonic tomography of optical vortices

We present a method for analyzing the wavefront of optical vortices that does not involve interferometry but rather uses surface plasmon polaritons (SPPs). We employ a subwavelength slit in a gold film to cut slices from an optical vortex beam and measure the diffraction of the generated SPPs by scattering them off a second slit. By moving the slits across the vortex beam, we create a tomogram, from which we can determine the vortex charge of the incident beam at a glance. We present results for vortex beams of integer- and half-integer-vortex charge.     

Numerical solution of the reduction problem when the ratio of the half-widths of the slit function and the observed contour is close to unity

The question of obtaining a solution that is stable in the presence of initialdata error for the reduction problem in Raman scattering for various ratios of the half-widths of the slit function and the observed contour is discussed. It is shown that when the ratio of the half-widths is close to unity, a stable solution in the class of well-posed problems can be obtained by application of the discrete Fourier transform.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 92–96, September, 1984.     

Sub-wavelength interference in the field assisted by surface plasmons

We present a theoretical study of the optical transmission from a thin metallic double slit. The second-order correlation function as a function of the displacement of the detectors for different values of slit separation is studied. It is shown that surface plasmons excited at one slit and propagating to the other slit modulate the coincidence counts with the variation of slit separation. Sub-wavelength interference effect has also been observed for the field assisted by surface plasmons. It is also shown that the second order interference-diffraction pattern changes with slit separation and at some particular value of slit separation it changes into the Hanbury Brown and Twiss (HBT) effect.     

Supercontinuum and third-harmonic generation accompanying optical filamentation as first-order scattering processes

It is demonstrated numerically that the supercontinuum generation and third-harmonic generation that accompany optical filamentation in nonlinear dispersive bulk media can be described as first-order scattering processes akin to the first Born approximation. In particular, for an incident ultrashort pulse the angularly resolved spectrum of the transmitted pulse is shown to be accurately determined using first-order scattering of the incident field from the nonlinearly modified refractive index due to the optical filament. Thus, although an optical filament is a highly nonlinear object, the accompanying supercontinuum generation and third-harmonic generation are driven parametrically by the filament and have negligible back action upon it.     

Dual mode near-field scanning optical microscopy for near-field imaging of surface plasmon polariton

In this paper, we theoretically and experimentally demonstrate that metal coated apertured probes are efficient near-field probes on surfaces with high reflectivity for the scattering as well as for the collection mode near-field scanning optical microscopy (NSOM). We show that a blunt apertured metal coated tip is very effective in suppressing image dipoles which affect strongly the signals scattered from frequently used sharp metal tips or gold nanoparticle attached probes. By using a simultaneous collection and scattering mode (dual mode) NSOM we measure the near-field images of surface plasmon polariton (SPP) launched from a slit. The collection mode measures propagating SPP along lateral distance in a long scan range with high signal-to-noise ratio, and the scattering mode measures the polarization resolved near-field of SPP. Comparisons of the measured data obtained in the dual mode enable to easily characterize SPP and to separate the measured near-field into the propagating SPP and the directly transmitted light.     

A study on the effect of filling factor for laser action in dielectric random media

In a random system composed of dielectric materials, laser action is expected to occur from the light localization caused by multiple scattering and interference effect. The wavelengths at which the laser oscillation occurs in random media depend on the mean free path of continuous scattering. Since the mean free path of continuous scattering is dependent on the filling factor, it is important to investigate systematically the effect of the filling factor for the laser action. In the present study, we calculate the Poynting vectors of the light emitted from two-dimensional random media consisting of dielectric rods with population inversion modeled by the negative imaginary part of relative permittivity. The spectra of the radiated Poynting vectors from the two-dimensional random media are shown for several different filling factors and for various values of population inversion. We try to find laser generation which occurs at low population inversion and discuss about the threshold of laser action occurring in dielectric structures with different filling factors. We also study the spacial distribution of the electric field amplitude in several frequency regions where light strongly amplifies.     

X射线散射法测量超光滑平面

介绍了掠入射X射线散射法(GXRS法)测量超光滑表面的原理及基于商业用X射线衍射仪改造而成的实验装置。以3片不同粗糙度的硅片作为实验样品,分别应用一级矢量微扰理论和改进的Harvey-Shack理论对其散射分布进行处理,所得结果与原子力显微镜测量结果基本相符。分析了探测器接收狭缝的宽度和入射光发散度对实验结果的影响,随着探测器接收狭缝宽度和入射光发散度的减小,测量误差呈指数迅速减小。在所测量的空间频率范围内,功率谱密度（PSD）函数的误差随频率的增加而减小。     

Transmission enhancement through a metallic slit assisted by low scattering loss corrugations

A method to obtain large transmission of light through a nano-metallic slit bordered by nano trenches is demonstrated theoretically. The model is based on the composite diffraction of evanescent waves (CDEW) theory and utilizes a single trench design to effectively convert free-space light into surface plasma waves (SPW). The effectiveness is confirmed by the finite difference time domain (FDTD) method. The SPW loss due to scattering by the trench is also analyzed. It is found that when the width of the trench is slightly larger than λ_spp/2, the SPW becomes localized and resonates at the bottom edges performing as a dipole-like radiation source. At this time, the propagating SPW suffers from high scattering loss. Trenches can be used to enhance the transmission of a nano-scaled slit while simultaneously preserving high conversion efficiency and low scattering loss. A nano-scaled slit bordered by 10 pairs of trenches can be enhanced by a factor as high as 16. It is determined that a device designed to have a large clear aperture of 15 μm would have an advantage in terms of alignment.     

Deflecting Atoms through a Submicron-Sized Slit with Near-Field Light

We report experiments on deflecting cold ⁸⁷Rb atoms by repulsive near-field light induced in a 200-nm-wide slit. The spatial profile is measured with a two-step photoionization scan. The number of outputted atoms from the slit increases by the amount of 40 ± 7.2% at a 5.1 ± 2.0° angle for the blue detuning of +1 GHz. We discuss the spatial profile involving an image of the atomic cloud by means of the scattering cross section.     

Transient stimulated Raman scattering in a two-component gas mixture

Generation of the first Stokes components of stimulated Raman scattering (SRS) in two-component gas mixtures, including the combination component (resulting from scattering of the first (second) Stokes component in the second (first) gas) is studied by numerical methods. The condition for efficient generation of the combination Stokes component is derived and interpreted. It is shown theoretically and by numerical simulation that the optimal ratio of the pressures for the transient SRS generation of the combination component is inversely proportional to the ratio of the Raman scattering cross sections of the two gases. The results of numerical simulation agree well with experimental data.     

The effect of the long-range order in a quantum dot array on the in-plane lattice thermal conductivity

Semiconductor quantum dot superlattices consisting of arrays of quantum dots have shown great promise for a variety of device applications, including thermoelectric power generation and cooling. In this paper we theoretically investigate the effect of long-range order in a quantum dot array on its in-plane lattice thermal conductivity. It is demonstrated that the long-range order in a quantum dot array enhances acoustic phonon scattering and, thus leads to a decrease of its lattice thermal conductivity. The decrease in the ordered quantum dot array, which acts as a phonon grating, is stronger than that in the disordered one due to the contribution of the coherent scattering term. The numerical calculations were carried out for a structure that consists of multiple layers of Si with layers of ordered Ge quantum dots separated by wetting layers and spacers.     

Spectral dynamics studies on the supercontinuum channel of femtosecond laser pulses propagation in air

We present the spectral dynamics investigations of supercontinuum generation from 2.6 TW femtosecond laser pulses propagation in air. The measured spectra in the supercontinuum channel show a large amount of oscillating structure, which is mostly contributed from four-wave mixing, stimulated Raman scattering and the electronic mechanism self-phase modulation. The temporal coherence length is almost the same as 0.45 ps for each spectral component with the same spectral width of supercontinuum that is confirmed with a Michelson interferometer. The spatial coherence property of supercontinuum is measured by a Young’s double slit diffractometer, which demonstrates that supercontinuum preserves a transverse coherence of about 144 μm because of the divergence of the supercontinuum channel. PACS  42.62.Fi; 42.68.Ay; 43.25.Jh     

Fourier-domain angle-resolved low coherence interferometry through an endoscopic fiber bundle for light-scattering spectroscopy

We present a novel endoscopic fiber bundle probe incorporated in a Fourier-domain angle-resolved low coherence interferometry system for the measurement of depth-resolved angular scattering distributions to permit the determination of scatterer size via elastic scattering properties. Depth resolution is achieved with a superluminescent diode via a Mach-Zehnder interferometer. The sample is illuminated with a collimated beam, and a Fourier plane image of the backscattered light is collected by a coherent fiber bundle. The angular scattering distribution relayed by the fiber bundle is mixed with the reference field and made to coincide with the input slit of an imaging spectrograph. The data collected are processed in real time, producing a depth-resolved angular scattering distribution in 0.37 s. The data are used to determine the sizes of polystyrene microspheres with subwavelength precision and accuracy.     

Development of acoustoelectric domains in zinc oxide with small inhomogeneities

The generation and development of acoustoelectric domains in slightly doped ZnO crystals (? ～ 30 Щcm) is studied by Brillouin scattering. The generation of multiple domains is observed which is found to be the reason for the lack of current oscillations in this material. From the distribution of the domains in space and time it is concluded, that a variation in ? is established along the sample. Furthermore it is shown, that for a proper interpretation of Brillouin scattering experiments, the divergence of the sound beam has to be considered. By the method of interpretation which is discussed in paragraph 4, Brillouin scattering experiments can also be used for the investigation of frequencies for which the scattered light is totally reflected if the geometry of Bragg scattering is used.