PV-400 Time-Interval Analyzing Electro-Optical Transducer with Wide-Format Photocathode and Picosecond Resolution Time

A new time-interval analyzing electro-optical transducer with 4 × 40 mm² photocathode, time resolution down to 2 psec, and spatial resolution down to 35 line pairs per millimeter is developed. The transducer is designed for use in the study of the spectra of optical radiation in the dynamic mode. The electro-optical system has a four-electrode design. The accelerating mesh electrode is situated a distance of about 1 mm from the photocathode. The deflecting plates are supplied with electron traps, making possible beam suppression.     

Ultrasensitive liquid refractometer based on a Mach-Zehnder micro-cavity in optical fibre fabricated by femtosecond laser-induced water breakdown

Abstract

A Mach–Zehnder (MZ) micro-cavity with two symmetric openings in single mode fibre (SMF) was fabricated by femtosecond laser-induced water breakdown. The micro-cavity is rightly across half of the fibre core, and the opening size of the micro-cavity is 10 μm × 100 μm. The micro-cavity and the remaining half of the fibre core constitute two arms of the Mach–Zehnder interferometer (MZI). The MZI with micro-cavity immerged in water shows perfect interference spectrum due to the regular shape and smooth internal surface of the micro-cavity. The insertion loss is only –8 dB and the contrast of one MZI peak reaches more than 40 dB. The MZI with micro-cavity in SMF can be used as an ultrasensitive liquid refractometer as its ultrahigh refractive index (RI) sensitivity (14296.98 nm/RIU), high RI resolution (1 × 10^?5 RIU), good linearity (99.62%) and low temperature crosstalk (0.04 nm/°C).     

Modulation Transfer Function Assessment for Sampled Imaging Systems: A Generalization of the Line Spread Function

Abstract

The line spread function is a classical figure of merit for the modulation transfer function assessment of an optical system. However, this test cannot be directly applied to sampled imaging systems as they often exhibit aliasing effects. The purpose of this paper is to define a new figure of merit which allows the characterization of the transfer of all spatial frequencies even those which are placed after the Nyquist frequency. An experiment has been carried out to demonstrate the effectiveness of this new test.     

The effect of visual perception on the required performance of imaging systems

Abstract

Current performance measures for infrared imagers are applicable to linear mechanically scanned systems but not to those with focal plane arrays of detector elements, because these are nonlinear due to aliasing. The performance of an imager affects the ability of an observer to perform perception tasks using it. Psychophysical trials have been undertaken in an attempt to identify more appropriate performance measures. Simple shapes degraded by various degrees of Gaussian blurring and pixelation were selected at random and displayed on a computer monitor. A correlation has been found between the probability of recognition of an image and a quantity called ‘recognition contrast’ (C _R). This is related to the shape observed and a template of the equivalently degraded alternative shape most similar to it. This quantity C _R was refined following trials in which spatial noise was added to Gaussian blurred images. C _R is calculated from information about each of the two images and is directly proportional to the sensitivity index d' obtained from probability measurements. The results described are believed to have a wide range of applications such as in defining image quality and performance measures for imaging equipment.     

Improvement in device performance from a mixture of a liquid crystal and photosensitive acrylic prepolymer with the photoinduced vertical alignment method

Abstract

In a multicomponent nematic liquid crystal (NLC) mixture of a liquid crystal (negative-type NLC) and a photosensitive acrylic prepolymer, photopolymerization upon UV irradiation induces the separation of the LC and photosensitive acrylic prepolymer layers, thereby leading to a vertical arrangement of LC molecules. In this study, we propose a simple vertical alignment method for LC molecules, by adding a chiral smectic A (SmA?) liquid crystal having homeotropic texture characteristics to an NLC mixture solution. Measurements of electro-optical properties revealed that the addition of the SmA? LC not only strengthened the anchoring force of the copolymer alignment film surface, but also significantly enhanced the contrast ratio (～73%), response time and grayscale switching performance of the device.     

Electrical properties and morphology of obliquely deposited electrochromic WO3 films

A thin film of WO₃ deposited obliquely (θ≈50°) improves the electro-optical response times of an electrochromic display device based on a proton insertion-extraction mechanism. The difference in the response times is attributed to morphological differences as revealed by electron microscope observations. WO₃ films were deposited normally and obliquely, by electron beam gun deposition technique so as to have comparable resistivities in vacuum of about 10^-4 Torr. The resistivity of these films was varied in different ways by exposure to atmospheric air in a controlled manner. Systematic and comparative investigations of the variation in resistivity of these films showed that the resistivity increased in the first stage (10^-4 Torr to atmospheric pressure), attained a maximum value and decreased thereafter in the second stage on long exposure to the atmosphere. The initial increase was explained as the result of oxidation leading to better stoichiometry, limited by the process of uptake of water vapour (hydration). The latter effect was much less for normally deposited film; however, for obliquely deposited film it was much greater and resulted in a decrease in resistivity by three orders of magnitude more than for normally deposited film. The large degree of hydration in an obliquely deposited film was ascribed to its more porous nature, leading to faster electro-optical response times. It was concluded that the microstructure, the stoichiometry and the water content control the electro-optical response of WO₃ films.     

Analysis of high‐order finite elements for convected wave propagation

In this paper, we examine the performance of high‐order finite element methods (FEM) for aeroacoustic propagation, based on the convected Helmholtz equation. A methodology is presented to measure the dispersion and amplitude errors of the p‐FEM, including non‐interpolating shape functions, such as ‘bubble’ shape functions. A series of simple test cases are also presented to support the results of the dispersion analysis. The main conclusion is that the properties of p‐FEM that make its strength for standard acoustics (e.g., exponential p‐convergence, low dispersion error) remain present for flow acoustics as well. However, the flow has a noticeable effect on the accuracy of the numerical solution, even when the change in wavelength due to the mean flow is accounted for, and an approximation of the dispersion error is proposed to describe the influence of the mean flow. Also discussed is the so‐called aliasing effect, which can reduce the accuracy of the solution in the case of downstream propagation. This can be avoided by an appropriate choice of mesh resolution. Copyright © 2013 John Wiley & Sons, Ltd.     

Correspondence

Abstract

According to the Nyquist sampling theorem, a large number of sampled images and small intervals between capturing cameras should be met for rendering high quality virtual views without aliasing, which is hard to realize in practice. Therefore, achieving a balance between multi-view data capturing and quality of the rendered view remains as open problems. To solve this problem, we analysed the spectral bounds of the scene and designed a reconstruction filter. A proper number for rendering and a three-dimensional surface describing the relation between multi-view data capturing and quality of the rendered view were derived. Experimental results for both the modelled scene and the real scene show that only about 20% of sample images are needed compared with Nyquist sampling, while the quality of the rendered view remains higher than that of a Nyquist sampled comparison.     

Microwave Near-Field Imaging with Open-Ended Waveguide—Comparison with Other Techniques of Nondestructive Testing

Abstract

The results of an experimental study of microwave imaging with an open-ended waveguide at 30 GHz for NDE of dielectric materials are presented. Using a hybrid measurement method, the near-field point spread function is investigated. Improvement of sensitivity and resolution via deconvolution also is discussed. A comparison of results obtained with more prominent NDE methods as ultrasonics, X-rays, and thermal waves demonstrates the performance of the technique.     

Influence of luminance and resolution on the perceived quality of black-and-white images on soft displays

Abstract

The perceived quality of an image displayed on a computer monitor depends on a number of different factors that can affect viewers' preferences. Two of these are the luminance of the monitor display and the resolution of the image. The effect of luminance is of interest for applications such as on-line access of images where the computer displays used for viewing these images could have different luminance settings. A relationship between cathode-ray tube (CRT) display luminance and resolution has been shown in previous studies. It was therefore interesting to investigate whether there is a relationship between image resolution and CRT display luminance on perceived image quality. Image resolution is related to the image file size, which is an important factor for applications such as on-line access of images. This work used a CRT display to study the effect of the above-mentioned factors on the perceived quality of the displayed image. Three sets of black-and-white images, each set with a different resolution, were presented to observers at three brightness settings of the computer monitor. Results are discussed regarding the effect of monitor display luminance and image resolution on perceived image quality and the interaction between them. Evaluation of results is further extended to the influence of the different backgrounds of the images. The scene content of the images was also shown to affect the viewers' judgement.     

Numerical techniques on improving computational efficiency of spectral boundary integral method

Numerical techniques are suggested in this paper, in order to improve the computational efficiency of the spectral boundary integral method, initiated by Clamond & Grue [D. Clamond and J. Grue. A fast method for fully nonlinear water‐wave computations. J. Fluid Mech. 2001; 447 : 337–355] for simulating nonlinear water waves. This method involves dealing with the high order convolutions by using Fourier transform or inverse Fourier transform and evaluating the integrals with weakly singular integrands. A de‐singularity technique is proposed here to help in efficiently evaluating the integrals with weak singularity. An anti‐aliasing technique is developed in this paper to overcome the aliasing problem associated with Fourier transform or inverse Fourier transform with a limited resolution. This paper also presents a technique for determining a critical value of the free surface, under which the integrals can be neglected. Numerical tests are carried out on the numerical techniques and on the improved method equipped with the techniques. The tests will demonstrate that the improved method can significantly accelerate the computation, in particular when waves are strongly nonlinear. Copyright © 2015 John Wiley & Sons, Ltd.     

Pockels' Effect in α-quartz

The dispersion of the two linear electro-optical constants r ₁₁ and r ₄₁ (clamped) of f -quartz is obtained from the experimentally observed electro-optical birefringence. The half-wave voltages at different wavelengths are presented for the two orientations studied.     

Optical properties of BaTiO3/ZnO heterostructures under the effect of an applied bias

We report electro-optical measurements of BaTiO₃/ZnO heterostructures grown by pulsed laser deposition. The optical properties of the heterostructures were examined with and without an applied bias. A change in the heterostructure optical properties is found and attributed to a linear electro-optical effect causing a change in the band gap. Moreover the formation of an electric polarization in the BaTiO₃ layer causes a remanent change in the dielectric function if the bias is removed. The change could be estimated to be around 5 meV.     

Adjustable active optical low-pass filter

This paper presents an active optical low-pass filter (AOLPF) capable of changing the resolution of an imaging system on demand in order to remove aliasing noise from a sampling image. This is advantageous over conventional optical low-pass filters, which are fixed image-blurring optical components that are built into the imaging system, in order to remove aliasing in the image. Furthermore, conventional filters smear images regardless of the presence or lack of high spatial frequency, which can exceed the Nyquist limit of the sensor. On the contrary, the proposed AOLPF can dynamically adjust the modulation transfer function of an imaging system to eliminate aliasing artifacts. In addition, this filter can be turned off in the absence of high spatial frequency to maximize resolution and prevent unnecessary blurring of the sampling image.     

基于移动麦克风阵列的稳态声源识别

基于波束形成的麦克风阵列声源识别技术存在识别低频声源分辨率低、识别高频声源易产生空间混叠的问题,影响了声源识别的准确性。对于稳态声源,本文提出两种麦克风阵列移动方法,即改变麦克风阵列中心位置、调整测量距离来提高低频声源识别分辨率,和采用旋转麦克风阵列进行多次测量的方法来抑制高频声源识别中的空间混叠,从而达到使用较少麦克风提高声源识别性能的目的,并通过仿真和实验验证了此方法的有效性。     

On telescope performance evaluation

Abstract

We analyse the imaging performance of synthetic-aperture optical systems (diluted aperture and segmented aperture) using the modulation transfer function. We select a single figure-of-merit, the functional cut-off frequency, over the traditional cut-off frequency, as the most useful one for assessing the optical performance of an instrument for its imaging capacity. A simplified aperture layout is proposed with the performance equivalent to that of the Keck telescope, incorporating a smaller number of segments. The detailed analysis in the spatial frequency plane leads us to observe that the central ring of the hexagons in the Keck telescope does not contribute to its resolution.     

光电经纬仪结构动态特性研究

光电经纬仪的结构动态特性是设计光电经纬仪的重要依据。用临界转速法建立了光电经纬仪的结构动态特性模型,讨论了光电经纬仪转速与轴系横向振动固有频率的关系:光电经纬仪的临界转速在数值上与经纬仪横向自由振动的固有频率相同,且光电经纬仪的固有频率只与其轴系挠度的平方根成反比。研究表明,提高光电经纬仪伺服控制系统带宽有4个途径:1) 增大光电经纬仪的固有频率;2) 对结构谐振进行补偿;3) 使用电流反馈;4) 使用加速度和速度反馈等。     

A study of the wide ferroelectric phase in mixtures of chiral and non-chiral tilted smectic C-type liquid crystals

A new liquid crystal of a siloxane dimer with an achiral swallow-tail, C11Si2C11, D, was synthesized and mixed with a chiral material as a chiral dopant, 4′-[11-(1,1,2,2,3,3,3-heptamethyltrisiloxanyl)undecyloxy]biphenyl-4-carboxylate, C11Si3, C, to prepare binary mixtures for this study. All mixtures possess the ferroelectric chiral smectic C phase over a broad temperature range. For respect compound C11Si3, the temperature range of the SmC* phase was only 72.6 °C, and was increased upon the addition of dimer C11Si2C11. The electro-optical properties of the SmC* phase, such as tilt angle, dielectric permittivity and switching behavior were also measured. It appeared that the mixtures had a similar viscosity, but the switching time was decreased due to the larger P_s, which was caused by an increased proportion of C11Si3. Therefore, the mixtures revealed a similar tilt angle at around 37.5° at temperatures within their respective mesophase temperature ranges. As a consequence, the correlation between the electro-optical properties and mixture proportion was determined.     

Spiral hyperlens with enhancements of image resolution and magnification

Abstract

A subwavelength spiral hyperlens that is able to image beyond the diffraction limit is studied. The spiral hyperlens is made from an anisotropic metamaterial with a hyperbolic dispersion relation in which the evanescent wave is converted into a propagating wave. Therefore, the propagating wave can be processed by conventional optical systems outside of the spiral hyperlens. The possibility of using a cylindrical hyperlens for overcoming the diffraction limit has been proven analytically and experimentally. In this study, we designed two types of spiral hyperlenses composed of a spiral periodic stack of silver and alumina multilayers. A spiral hyperlens utilizes the spiral geometry to magnify the objects. In comparison with a cylindrical hyperlens, a spiral hyperlens has improved performance in terms of higher image resolution and better image magnifications. Numerical simulations illustrate that the far-field imaging resolution of cylindrical spiral hyperlens is no greater than 110 nm at 365 nm working wavelength.     

高清摄像机分辨率测试方法研究

本介绍了ISO 12233电子相机分辨率测试图的结构与功用，讨论了有关分辨率的若干基本概念，还讨论了借助该测试图对高清摄像机的分辨率(目力分辨率、极限分辨率、空间频率响应、混叠比)进行测试的方法。