Hybrid-integrated prism array optoelectronic targeting system

This investigation proposes a cost-effective, compact, and robust optoelectronic targeting system for measuring ballistic impact velocity and the distribution of projectile motion. The major elements of this system are four photo-gates hybridized by compound one-dimensional prism array and analog/digital electronic components. The number of light sources and photodetectors used in a photo-gate was reduced to one pair of light source and photodetector. The average velocity and location of the projectile are determined according to the measured time intervals (10^-8 s) passing each pair. The system can accurately measure the velocity of a bullet as it leaves a gun barrel, as well as the velocity at specific points along the trajectory outside the firearm. Additionally, the system uses a widespread low-powered laser pointer as a light source. Compared with other optoelectronic targeting systems that use high-powered lasers, the proposed system is both economical and safe.     

Diffraction of partially coherent X‐rays in clessidra prism arrays

When small triangular prisms are arranged in arrays which have an overall appearance like an hourglass (in Italian: clessidra) they can focus X‐rays owing to a combined action of diffraction and refraction. From the optical point of view these objects can be regarded as a Fresnel variant of concave transmission lenses. Consequently they can provide larger apertures than purely refractive lenses. However, one has to recognize that clessidra lenses will strongly diffract as the lens structure is periodic in the direction perpendicular to the incident beam. In experiments the diffraction is reduced because it is difficult to illuminate the large apertures with a full spatially coherent wavefront. So the illumination is at best partially coherent. In order to interpret available experimental data for this condition, diffraction theory has been applied appropriately to the clessidra structure, taking into account the limited spatial coherence. The agreement between the theoretical simulations and experimental data is very good, keeping the lens properties at their projected values and allowing for only two free model parameters. The first is the lateral spatial coherence; the second is a lens defect, a rounding of all edges and tips in the structure. Both values obtained from the simulations have been found to be in agreement with expectations.     

Multi-directional lateral shearing interferometer based on rotatable prism pairs

The common camera lens usually includes the spherical glass/plastic lens and aspheric glass/plastic lens. However, spherical/aspheric shape measurement is still a key problem in the process of optical lens fabrication. At present, the in-process measurement of spherical/aspheric shape is conducted mainly by the probe-contacting method. But after a long time, its probe could be scratched severely and cause some big errors. Laser shearing interferometry is a good substitute to some degree. Nevertheless, it is not convenient for general shearing interferometer to carry out the in-process measurement because it is only suitable for certain kind of spherical/aspheric with respect to aperture or asperity. Here a new lateral shearing interferometer is proposed to solve the described problems. It is based on two Jamin plates and rotatable prism pairs which are used not only for shearing displacement and direction, but also for fringe period and tilt degree, in order to meet requirements of various spherical/aspheric shapes or asperities. The new interferometer features a simple optical structure and two symmetric light paths, which makes its system with minimal error. The relation between shearing displacement, fringe period and prism angle of rotation is given in this paper. And the error source is primarily from the manufacture errors of prisms and plates. The final experiments show that one can achieve good-quality fringe patterns according to the requirement of measurement, concerning the shearing direction, shearing displacement, fringe period, tilt degree, etc.     

Diffraction theory applied to X‐ray imaging with clessidra prism array lenses

Clessidra (hourglass) lenses, i.e. two large prisms each composed of smaller identical prisms or prism‐like objects, can focus X‐rays. As these lenses have a periodic structure perpendicular to the incident radiation, they will diffract the beam like a diffraction grating. Refraction in the prisms is responsible for blazing, i.e. for the concentration of the diffracted intensity into only a few diffraction peaks. It is found that the diffraction of coherent radiation in clessidra lenses needs to be treated in the Fresnel, or near‐field, regime. Here, diffraction theory is applied appropriately to the clessidra structure in order to show that blazing in a perfect structure with partly curved prisms can indeed concentrate the diffracted intensity into only one peak. When the lens is entirely composed of identical perfect prisms, small secondary peaks are found. Nevertheless, the loss in intensity in the central peak will not lead to any significant widening of this peak. Clessidras with perfect prisms illuminated by full coherent X‐ray radiation can then provide spatial resolutions, which are consistent with the increased aperture, and which are far below the height of the single small prisms.     

Effect of coherence property of incident light on prism waveguide coupling

The accurate reflection coefficient of prism waveguide coupler that takes coherence property of incident light into account is obtained at first. Based on the reflection coefficient, the effect of coherence property of incident light on prism coupling is discussed in this work. It is shown that extra damping in waveguide caused by the coherence property is larger for high-order resonant mode than that for low-order mode. For 100 fs Gaussian pulses incidence, the reflected spectra at different resonant modes are obtained theoretically and experimentally, which show that coherence property has a strong effect on prism coupling at high-order modes.     

Optical design for enhanced prism type fingerprint scanner image contrast with asymmetrical aspheric lens

The design of optical prism fingerprint scanner with aspheric lens is researched. We propose a modified structure for optical prism fingerprint scanner, which has an asymmetrical aspheric lens on the output plane. It is numerically shown under elliptic valley similar fingerprint model that the optical image qualities of such a scanner are better than the scanner with symmetrical aspheric lens. When the fingerprint range is 15 mm, the results show that the minimum image contrast is 0.49 for an optical prism with asymmetrical aspheric lens, much better than a symmetrical aspheric lens with 0.20. The relative illumination variation is from 0.62 to 1.00 for optical prism with asymmetrical aspheric lens, and for the symmetrical aspheric lens it is 0.35 to 1.00. We conclude that an optical prism with asymmetrical aspheric lens is better than an optical prism with symmetrical aspheric lens.     

On the use of clessidra prism arrays in long‐focal‐length X‐ray focusing

Clessidra (hour‐glass) X‐ray lenses have an overall shape of an old hour glass, in which two opposing larger triangular prisms are formed of smaller identical prisms or prism‐like objects. In these lenses, absorbing and otherwise optically inactive material was removed with a material‐removal strategy similar to that used by Fresnel in the lighthouse lens construction. It is verified that when the single prism rows are incoherently illuminated they can be operated as independent micro‐lenses with coinciding image positions for efficient X‐ray beam concentration. Experimental data for the line width and the refraction efficiency in one‐dimensional focusing are consistent with the expectations. Imperfections in the structures produced by state‐of‐the‐art deep X‐ray lithography directed only 35% of the incident intensity away from the image and widened it by just 10% to 125 µm. An array of micro‐lenses with easily feasible prism sizes is proposed as an efficient retrofit for the refocusing optics in an existing beamline, where it would provide seven‐fold flux enhancement.     

An accurate method to calculate the negative dispersion generated by prism pairs

Based on the principle of diffraction for light transport in prisms, we figured the physical image for light beams passing through a pair of prisms. The mechanism to induce negative dispersion was analyzed and the numerical expression of optical path length was provided. From a series of mathematical equations, we calculate the quantity of negative dispersion, such as the second- and third-order dispersion, induced by prism pairs. Compared with the expressions of Fork et al. (Opt. Lett. 9(5) (1984) 150), our equations can lead to accurate results and reasonably elucidate the implication of dispersion.     

Set the controls for the heart of the Sun

In this paper we describe experiments conducted with high-power lasers that are attempting to replicate, for a very short time and in miniature, conditions found in the Sun. Experiments to date have reached conditions in the outer part of the Sun. To reach the Sun's centre requires compression of material to very much greater than solid density and heating to over ten million degrees. To achieve this, a new class of experiments and a new generation of high-power lasers are required.     

Fiber grating prism for true time delay beamsteering

This article presents theoretical designs for a beamsteerer that uses one laser source whose wavelength is electrically tuned. Transmit/receive beamsteering of a phased-array antenna is obtained with prism-shaped arrays of fiber Bragg gratings or with waveguided gratings integrated in a semiconductor chip. An analysis of chirped and uniform grating requirements is given.     

Non-classical neutron beams for fundamental and solid state research

The curious dual nature of the neutron, sometimes a particle, sometimes a wave, is wonderfully manifested in the various non-local interference and quantum contextuality effects observed in neutron interferometry. Non-classical states may become useful for novel fundamental and solid state research. Here we discuss unavoidable quantum losses as they appear in neutron phase-echo and spin rotation experiments and we show how entanglement effects in a single particle system demonstrate quantum contextuality. In all cases of interactions, parasitic beams are produced which cannot be recombined completely with the original beam. This means that a complete reconstruction of the original state would, in principle, be impossible which causes a kind of intrinsic irreversibility. Even small interaction potentials can have huge effects when they are applied in quantum Zeno-like experiments. Recently, it has been shown that an entanglement between external and internal degrees of freedom exists even in single particle systems. This contextuality phenomenon also shows that a quantum system carries much more information than usually extracted. The path towards advanced neutron quantum optics will be discussed.      

A semi-empirical formula for the neutron total cross section and the interpretation of the empirical formula forA ⩾ 40

Weaknesses in Angeli and Csikai’s interpretation of their empirical formula for the neutron total cross section (σ _T) are pointed out. Using the Fourier-Bessel re-presentation of the scattering amplitude a semi-empirical formula forσ _T is obtained which has greater applicability and also explains the success of the empirical formula for mass numberA ⩾ 40 in terms of the established trends in neutron optical potential parameters.     

高精度激光参数测量系统中衰减系统的研究与评价

 分析了楔形镜和中性玻璃衰减片组对光束的衰减原理,采用反射式楔形镜作为无像差定量衰减器,并同时使用中性玻璃衰减片组微调光束能量。实验测量了LD泵浦激光模式发生器基模和高阶模条件下激光束的M­²因子,结果表明：楔形镜反射式衰减器对光束质量无显著影响,将楔形镜第一次表面反射作为无像差定量衰减,入射角在0~55°范围内,单棱镜表面反射光束能量为入射光能量的4.3%,通过多块组合可以得到更大的衰减;可采用中性玻璃衰减片组对激光光束的衰减进行精细控制,使其满足CCD探测器动态范围要求。该结论可为高精度激光参数测量装置光衰减系统的研制提供理论依据。     

角锥棱镜激光谐振腔的基本特性

 分析了角锥棱镜对光束的相位变换作用，带二面角误差的角锥棱镜可等效于6块光楔的组合，其楔角的大小和方向由二面角误差决定。对在腔内往返传输的光线在镜面上的位置进行了分析，结果表明：3个二面角误差相同且不为零的角锥棱镜构成的谐振腔为约束非稳腔。用Fox-Li迭代法数值模拟得到了不同棱镜二面角误差情况下的谐振模式。模拟结果表明：圆形镜腔情况下基本振荡模式接近于TEM₀₃模的拉盖尔高斯光束；当3个二面角误差不相同时，模式中各个区域的强度分布不对称。采用3个二面角误差基本接近且绝对值较小的棱镜可以提高光束质量。     

Refraction in plane-parallel plate—Reconsideration of method of measurement of refractive indices

The prism (minimum deviation) method of measurement of refractive indices in solids has a couple of disadvantages including problems associated with manufacturing of a good prism itself. Besides this method is unsuitable to be used in piezo- and electro-optical experiments when one needs to achieve so-called homogeneous distribution of an interaction (electric field, stress, strain) within the sample. Besides, worked out with a large expenditure of energy and cost, the prism is usually useless in other applications (destructive method). Therefore, an “elder” method of measurement of refractive indices by measuring shift of the refracted beam of light in a plane-parallel plate has been reconsidered in this paper. The sample itself may be a cuboid (if one wishes to measure all of three principal refractive indices in optically biaxial crystal), or just a crystalline boule in which one is cutting off the conical and tail parts and by suitable mechanical treatment (lapping and polishing) reveals a pair of plane parallel surfaces properly oriented to crystallographic (or principal axes of the optical indicatrix) directions. In such case, however, one can only measure one (isotropic crystals) or two (optically uniaxial crystals) refractive indices. However, in case of this method as opposed to the prism method one can repeat the measurement a couple of times, e.g. after a series of consecutive annealing, when this is either impossible or undesirable to cut the boule into smaller pieces prior to the final annealing (nondestructive method). The error depends on the angle of incidence and on sample (boule) thickness and is usually of the order of 0.001. However, in the future it is expected that the error can be reduced by implementing an electronic readout of the beam shift below 1 μm. Working of the method has been illustrated with a couple of examples in GdCOB (biaxial), LiNbO₃ (uniaxial) and YAG:Cr,Mg (isotropic) crystals.     

三元结构双反射平行分束偏光镜设计

为了节省冰洲石晶体材料,并实现两束偏振光的平行输出,采用冰洲石与光学玻璃组合的方法,给出一种双反射形式平行分束偏光镜的新设计。该棱镜为ZBaF3玻璃中间加冰洲石晶体薄片的三元结构,采用溴代萘胶合;选择合适的结构角,令电矢量振动方向相互垂直的两束偏振光分别在前胶合面、后端面发生全反射,并垂直上端面平行出射。实验测试表明,棱镜的透射比高于80%,消光比优于10-3。该设计在节省冰洲石晶体前提下,保持了良好的性能。     

角锥棱镜激光谐振腔的基本特性

分析了角锥棱镜对光束的相位变换作用,带二面角误差的角锥棱镜可等效于6块光楔的组合,其楔角的大小和方向由二面角误差决定。对在腔内往返传输的光线在镜面上的位置进行了分析,结果表明：3个二面角误差相同且不为零的角锥棱镜构成的谐振腔为约束非稳腔。用Fox-Li迭代法数值模拟得到了不同棱镜二面角误差情况下的谐振模式。模拟结果表明：圆形镜腔情况下基本振荡模式接近于TEM03模的拉盖尔高斯光束;当3个二面角误差不相同时,模式中各个区域的强度分布不对称。采用3个二面角误差基本接近且绝对值较小的棱镜可以提高光束质量。     

An empirical formula for scattered neutron components in fast neutron radiography

Scattering neutrons are one of the key factors that may affect the images of fast neutron radiog- raphy. In this paper, a mathematical model for scattered neutrons is developed on a cylinder sample, and an empirical formula for scattered neutrons is obtained. According to the results given by Monte Carlo methods, the parameters in the empirical formula are obtained with curve fitting, which confirms the logicality of the empirical formula. The curve-fitted parameters of common materials such as <'6>LiD are given.     

Bragg prism monochromator and analyser for super ultra-small angle neutron scattering studies

We have designed, fabricated and operated a novel Bragg prism monochromator-analyser combination. With a judicious choice of the Bragg reflection, its asymmetry and the apex angle of the silicon single crystal prism, the monochromator has produced a neutron beam with sub-arcsec collimation. A Bragg prism analyser with the opposite asymmetry has been tailored to accept a still sharper angular profile. With this optimized monochromator-analyser pair, we have attained the narrowest and sharpest neutron angular profile to date. At this facility, we have recorded the first SUSANS spectra spanning wave vector transfers Q ～ 10^?6 Å^?1 to characterize samples containing agglomerates up to tens of micrometres in size.     

用于干涉光谱仪中的新型Wollaston 棱镜系统

提出了一种用于干涉光谱仪中的新型Wollaston棱镜系统———带反射镜的Wollaston棱镜系统。对其结构及光束在其中的传播特性进行了深入分析,并对两束光的光程差进行了计算机模拟。结果表明光程差与入射点位置的关系具有极好的线性,并且所得光程差的动态范围为同类装置的二倍。研究结果为偏振型空间调制干涉光谱仪的设计和应用提供了理论依据。