Rigorous and approximate analysis of metallic gratings in soft X-ray and EUV regions

Abstract

In deep ultraviolet and soft X-ray regions the complex refractive indices of metals differ substantially from their values in the visible region of the spectrum. The implications of this fact are analysed for metallic gratings illuminated by electromagnetic fields with wavelengths ranging from soft X‐rays to near infrared, concentrating on short wavelengths. In particular, we study metal-stripe gratings (linear polarizers for visible light) by rigorous diffraction theory to determine the short-wavelength region in which a combination of the geometrical thin-element approximation and the theory of single-layer films can be applied. Then we study inductive grid filters for protection of X-ray detectors from infrared radiation in space applications.     

Fingerprint orientation alignment and similarity measurement

Abstract

In this paper, an algorithm for fingerprint orientation alignment is proposed in which a fingerprint is aligned to a particular direction according to its ridge flows. The algorithm works equally well for different types of fingerprints, including the type with no reference points. Aligned fingerprint images provide a lot of useful information for various applications. To demonstrate the use of such information, a fingerprint similarity measurement system is developed in which fingerprints are expressed by vectors with different elements derived from aligned images. When given two fingerprints, this system can help determine which of the two is more similar to a third fingerprint and which one is less similar by calculating distances among vectors. The alignment algorithm has been tested on 165 images in the NIST-4 fingerprint database. By rotating a test image in different degrees, 20 images are created. The alignment precision is calculated by an equivalent Euclidean norm, E(I), of the 20 rotated images to the original image. A smaller E(I) indicates a higher accuracy of the algorithm. The experimental results show that the average E(I) of these 165 samples is 1.234, and the spread of these 165 E(I)s is 1.1.     

Semi-automated detection of trace explosives in fingerprints on strongly interfering surfaces with Raman chemical imaging

We have previously demonstrated the use of wide-field Raman chemical imaging (RCI) to detect and identify the presence of trace explosives in contaminated fingerprints. In this current work we demonstrate the detection of trace explosives in contaminated fingerprints on strongly Raman scattering surfaces such as plastics and painted metals using an automated background subtraction routine. We demonstrate the use of partial least squares subtraction to minimize the interfering surface spectral signatures, allowing the detection and identification of explosive materials in the corrected Raman images. The resulting analyses are then visually superimposed on the corresponding bright field images to physically locate traces of explosives. Additionally, we attempt to address the question of whether a complete RCI of a fingerprint is required for trace explosive detection or whether a simple non-imaging Raman spectrum is sufficient. This investigation further demonstrates the ability to nondestructively identify explosives on fingerprints present on commonly found surfaces such that the fingerprint remains intact for further biometric analysis.     

Optical infrared remote sensors

Various kinds of remote sensors, active and passive, covering a significant part of the electromagnetic spectrum from ultraviolet to microwave regions have been developed for observation of earth for the purpose of resource survey. Several of the widely used remote sensors (in the visible and infrared region) beginning from photographic cameras to the modern-day linear imaging self-scanning sensors have been described with reference to the state-of-the-art, critical parameters, performance limitations etc. User requirements with regard to various system parameters of the remote sensors have been analysed. Some future trends in the development of remote sensors for spaceborne applications have been touched upon.     

Stretchable Cephalopod-Inspired Multimodal Camouflage Systems

Soft, mechanically deformable materials and systems that can, on demand, manipulate light propagation within both the visible and infrared (IR) regions of the electromagnetic spectrum are desirable for applications that include sensing, optoelectronics, robotics, energy conservation, and thermal management. However, the development of such technologies remains exceptionally difficult, with relatively few examples reported to date. Herein, this challenge is addressed by engineering cephalopod-inspired adaptive camouflage platforms with multispectral functionality. First, stretchable copolymer membranes that feature outstanding unstrained protonic conductivities of up to ≈90 mS cm⁻¹, demonstrate increases of ≈80% in their conductivities at strains of 200%, and exhibit no loss in electrical performance even under extreme elongations of 500% are described. Next, the membranes are used for the fabrication of mechanically and electrically actuated camouflage devices that function over an unprecedented spectral window; can simultaneously modulate their visible and IR specular-to-diffuse transmittance ratios by >3000-fold and >4-fold, respectively; feature rapid response times of ≈0.6 s; and exhibit good performance after repeated actuation. These findings may afford new scientific and technological opportunities not only for adaptive optics and photonics but also for any platform that can benefit from simultaneously controlling visible light and heat.     

Controlled supercontinua via spatial beam shaping

Abstract

Recently, optimization techniques have had a significant impact in a variety of fields, leading to a higher signal-to-noise and more streamlined techniques. We consider the possibility for using programmable phase-only spatial optimization of the pump beam to influence the supercontinuum generation process. Preliminary results show that significant broadening and rough control of the supercontinuum spectrum in the visible region are possible without loss of input energy. This serves as a proof-of-concept demonstration that spatial effects can controllably influence the supercontinuum spectrum, leading to possibilities for utilizing supercontinuum power more efficiently and achieving excellent spectral control.     

Radiation characteristics of a dense cesium plasma in the visible range

Calculations are made of the radiation spectrum from a cesium plasma column. It is shown that this plasma may serve as a light source with a high proportion of visible radiation and an almost continuous spectrum. The visible spectrum is formed mainly by bright recombination 6P and 5D continua whose thresholds are shifted in the long-wavelength direction. Pis’ma Zh. Tekh. Fiz. 23, 40–45 (December 26, 1997)     

Surface plasmon-polariton study of the optical dielectric function of zinc

Abstract

The optical dielectric function of zinc is measured by excitation of surface plasmon-polaritons on a silica prism coated in MgF₂ and zinc in the Kretchmann configuration and on a zinc-covered silica grating for a range of wavelengths in the visible spectrum. By exciting the surface plasmon at the zinc-MgF₂ or zinc-grating interfaces, the zinc is protected from oxidization and contamination. Comparison of angle-dependent reflectivities with either Fresnel's theory or grating modelling theory gives both the real and imaginary parts of the dielectric function of the zinc over the visible spectrum. The results compare very favourably with those obtained by other workers using more conventional methods for samples held in vacuum.     

Real and Altered Fingerprint Classification Based on Various Features andClassifiers

Biometric recognition refers to the identification of individuals through their unique behavioral features (e.g., fingerprint, face, and iris). We need distinguishing characteristics to identify people, such as fingerprints, which are world-renowned as the most reliable method to identify people. The recognition of fingerprints has become a standard procedure in forensics, and different techniques are available for this purpose. Most current techniques lack interest in image enhancement and rely on high-dimensional features to generate classification models. Therefore, we proposed an effective fingerprint classification method for classifying the fingerprint image as authentic or altered since criminals and hackers routinely change their fingerprints to generate fake ones. In order to improve fingerprint classification accuracy, our proposed method used the most effective texture features and classifiers. Discriminant Analysis (DCA) and Gaussian Discriminant Analysis (GDA) are employed as classifiers, along with Histogram of Oriented Gradient (HOG) and Segmentation-based Feature Texture Analysis (SFTA) feature vectors as inputs. The performance of the classifiers is determined by assessing a range of feature sets, and the most accurate results are obtained. The proposed method is tested using a Sokoto Coventry Fingerprint Dataset (SOCOFing). The SOCOFing project includes 6,000 fingerprint images collected from 600 African people whose fingerprints were taken ten times. Three distinct degrees of obliteration, central rotation, and z-cut have been performed to obtain synthetically altered replicas of the genuine fingerprints. The proposal achieved massive success with a classification accuracy reaching 99%. The experimental results indicate that the proposed method for fingerprint classification is feasible and effective. The experiments also showed that the proposed SFTA-based GDA method outperformed state-of-art approaches in feature dimension and classification accuracy.     

Effects of Aberrations on Transfer Functions Used in High Angular Resolution Astronomical Imaging

Abstract

In this paper we present the results of the effect of aberrations on the transfer functions used in the high-angular resolution astronomical imaging techniques of speckle interferometry, Knox-Thompson and bispectral imaging. The analyses are based on a computer simulation of imaging through atmospheric turbulence. The results show that as the seeing becomes worse, its effect dominates the behaviour of the transfer functions which tend to be independent of (small) optical aberrations. However, if the wavefront variation due to fixed aberrations is significant over r ₀-sized regions in the pupil (where r ₀ is the Fried parameter), the above transfer functions do depend on the aberration: in particular, the bispectral transfer function is relatively sensitive to odd aberrations, such as coma.     

Determination of the parameters of atmospheric gas clouds by radar methods at frequencies in the rotational spectrum

An analysis is made of a method of determining the parameters and coordinates of atmospheric gas clouds radar systems which can measure the attenuation of electromagnetic radiation power at a resonant absorption frequency. A possible technical application of these systems is indicated. This approach to the problem of controlling and monitoring the state of the atmosphere can describe the propagation dynamics of contamination in real time, which is extremely important for ensuring safety in regions liable to chemical contamination. After suitable development, the proposed method may provide the basis for remote monitoring by radar techniques and in principle, may also be used to study various types of nonreflecting objects possessing the property of resonant absorption. Pis’ma Zh. Tekh. Fiz. 23, 1–5 (December 26, 1997)     

Computation of the near-field pattern with the coupled-wave method for transverse magnetic polarization

Abstract

In this paper, an accurate method for computing the elecromagnetic field distribution in lamellar gratings is proposed. The method that relies on the rigorous coupled-wave analysis provides accurate numerical results and avoids possible sources of artefacts due to permittivity discontinuities. Its performance is analysed through various lamellar grating cases, including dielectric and metallic materials, the visible and near-infrared (1–10 μm) regions of the spectrum. Special attention is placed on field singularities which are in general present at the grating wedges for transverse magnetic polarization.     

牙齿图像识别技术在法庭科学中的应用

现代法庭科学中,人体特征识别主要采用下列四种技术：指纹识别、虹膜纹识别、DNA技术和牙齿形态识别。指纹载体是综合性有机物,虹膜是软组织,在重大灾难性案件中,他们极易毁坏,且我国尚未建立非犯罪人口档案库。DNA技术虽然鉴定精确,但成本高,检验周期较长,因此三种技术都有不足之处。相比之下在某些重大灾难性和刑事案件中牙齿形态鉴定法效果较好,本文对此作以介绍。     

A smart multifunctional polymer nanocomposites layer for the estimation of low-velocity impact damage in composite structures

A new smart polymer nanocomposite layer, based on semiconductor Cu₂S nanoparticles embedded into an amorphous polystyrene matrix, was developed for the detection of low-velocity impact damage on composite structures. This material exhibits a combination of optical and electro-magnetic properties, in way that it can be employed to visualize in quick and effective manner barely visible impact damage (BVID). In particular, based on the phenomenon of the photoluminescence, this layer showed specific light emission in the visible range of the electromagnetic spectrum under UV-light excitation at different wavelength. The results of a series of low-velocity impact tests illustrated a visible contrast colour on the damaged area, representing the flaw. In fact, the study of the optical characteristics of this smart material is of particular benefit for fast, cost-effective and in situ damage identification. Hence, once the impact location has been determined, the detailed information of the damage can be further investigated by others non-destructive techniques.     

Determination of the Optical Constants and Thickness of a Highly Absorbing Film Using the Attenuated Total Reflection Technique

Abstract

Theoretical analysis of the Kretschmann configuration for attenuated total reflection experiments shows that near the critical angle the reflectivity is strongly dependent upon the dielectric constants and thickness of a thin absorbing layer on the prism surface. Numerical calculations based on Fresnel's equations illustrate this clearly for thin absorbing films. Using this property of highly absorbing films it has then been possible to determine the optical constants of a thin film of phthalocyanine over the visible region of the spectrum.     

牙齿形态图像的记录与鉴定

在现代法庭科学中，人体特征识别主要采用下列四种技术：指纹识别、虹膜纹识别、DNA技术和牙齿形态识别。指纹载体是综合性有机物，虹膜是软组织，在重大灾难性案件中，他们极易毁坏，且我国尚未建立非犯罪人口档案库。DNA技术虽然鉴定精确，但成本高，检验周期较长，因此三种技术都有不足之处。相比之下牙齿形态鉴定法效果较好，本文对此作详细介绍。     

Research and development of metals for medical devices based on clinical needs

Abstract

The current research and development of metallic materials used for medicine and dentistry is reviewed. First, the general properties required of metals used in medical devices are summarized, followed by the needs for the development of α + β type Ti alloys with large elongation and β type Ti alloys with a low Young's modulus. In addition, nickel-free Ni–Ti alloys and austenitic stainless steels are described. As new topics, we review metals that are bioabsorbable and compatible with magnetic resonance imaging. Surface treatment and modification techniques to improve biofunctions and biocompatibility are categorized, and the related problems are presented at the end of this review. The metal surface may be biofunctionalized by various techniques, such as dry and wet processes. These techniques make it possible to apply metals to scaffolds in tissue engineering.     

Transitions in Presence of Short Laser Pulses

Abstract

Accurate numerical calculations are carried out to investigate the validity of the two-state approximation in the case of resonant interactions between electromagnetic radiation and atoms. Short pulses are considered and the presence of the atomic spectrum is modelled by introducing a third, non-resonant, state. We show that the harmonics of the pulse profile may play a significant role in the dynamics of the process and may cause energy non-conserving transitions between the atomic states.     

Polarization-based and specular-reflection-based noncontact latent fingerprint imaging and lifting

In forensic science the finger marks left unintentionally by people at a crime scene are referred to as latent fingerprints. Most existing techniques to detect and lift latent fingerprints require application of a certain material directly onto the exhibit. The chemical and physical processing applied to the fingerprint potentially degrades or prevents further forensic testing on the same evidence sample. Many existing methods also have deleterious side effects. We introduce a method to detect and extract latent fingerprint images without applying any powder or chemicals on the object. Our method is based on the optical phenomena of polarization and specular reflection together with the physiology of fingerprint formation. The recovered image quality is comparable to existing methods. In some cases, such as the sticky side of tape, our method shows unique advantages.