A spatially coherent achromatic fourier transformer

A specific configuration is proposed wherein two zone plates combined with an achromatic objective permits to cancel the chromatic scale factor as broad-band illumination is used in the Fraunhofer diffraction process. The set-up acts as a wavelength-independent Fourier transformer yielding an achromatic diffraction pattern of any complex pupil. Experimental results are also presented and demonstrate the ability of the system to work over the visible spectrum.     

An achromatic collimator for a multi-window flight simulator

Some flight simulators, known as multi-window simulators, are required to produce a wide field of view obtained by viewing a number of TV monitors through separate collimators. The extra requirement for shadowgraph projection of additional cueing information such as the sky and the horizon on to a dome above the pilot's head means that it is impossible to use the conventional concave mirror collimator. An alternative system is the Pancake Window but this gives insufficient light output.This paper describes the design of a three-element, all-plastic, one aspheric surface, achromatic, collimating lens which overcomes these problems. It is based on work carried out for the Royal Aircraft Establishment.     

An infrared photothermal beam deflection fourier transform spectrometer

A photothermal Fourier transform spectrometer built to accommodate a beam deflection detection system is described. The instrument, which can also function as conventional absorption FT spectrometer, and also a conventional FT photoacoustic spectrometer, covers the 3950−450 cm⁻¹ range. With quantities of l mg of powdered organic or inorganic material, infrared spectra of high quality can be obtained in minutes. Sample cells are not needed, and sample preparation is not required. The surface of truly massive objects may be examined, and surface studies may be carried out under rigorously controlled conditions.     

An electric-field cross-correlation fourier transform millimeter wave spectrometer

The principle and fundamental structure of a millimeterwave electric-field cross-correlation Fourier transform spectrometer are presented. In the spctrometer, two pseudorandom binary sequences (PRBS) with controllable phase variation are used to modulate individually two wide bandwidth microwave signals with variable phase delay are obtained. And the Fourier transform of the crosscorrelation function of these microwave signals is the cross-power spectrum. Some experimental results about the spectrometer are given in 8mm-wave range.Supported by Foundation of Specialities Opened to Doctorate Study.     

An ideal integrator in a radiometer

Radio Physics and Electronics Institute, Armenian Academy of Sciences. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 31, No. 8, pp. 903–906, August, 1988.     

Common-path achromatic rotational-shearing coronagraph

To suppress starlight for direct exoplanet observation, we propose a common-path achromatic rotational-shearing coronagraph (CP-ARC), which is an interferocoronagraph with an angular-adjustable field rotator. The CP-ARC aims to maintain unwanted detection of stellar light, which can be suppressed incompletely by interference because of the finite diameter of the star. Compared to the previous interferocoronagraph, which had a nonadjustable 180° field rotation, the proposed CP-ARC can improve the coronagraphic contrast by several orders if the CP-ARC is combined with medium or large telescopes where the companion-star separation is optically resolved by more than a few Airy radii. The CP-ARC is made robust against mechanical disturbances due to the common-path interferometer principle.     

Terahertz achromatic quarter-wave plate

Phase retarders usually present a strong frequency dependence. We discuss the design and characterization of a terahertz achromatic quarter-wave plate. This wave plate is made from six birefringent quartz plates precisely designed and stacked together. Phase retardation has been measured over the whole terahertz range by terahertz polarimetry. This achromatic wave plate demonstrates a huge frequency bandwidth (upsilonmax/upsilonmin approximately 7), and therefore can be applied to terahertz time domain spectroscopy and polarimetry.     

An ideal optical system with double-sided symmetry

A theory of an ideal optical system possessing double-sided (or planar) symmetry is developed using the projective transformations technique. In terms of the angular eikonal theory in the paraxial approximation, the theory developed is applied to the construction of a multimodular optical system consisting of ideal, at least two-component, optical systems with double-sided symmetry.     

一种新的消色像全息术

本文从全息再现像的物像关系出发,对准像面情况下,像点随波长及参考光源扩展的变化进行了研究.阐明了利用散射线光源作参考光使全可见光范围内的像叠加在一起,产生消色像全息图的基本思想,并引入了消色像域的概念.考虑到点基元全息图尺寸及人眼瞳孔对成像光束的限制,白光再现时,可以获得清晰、明亮、具有一定景深和相当视场范围的消色再现像.     

用于快速人脸识别的光学协处理器

设计了一种用于快速人脸识别的光学协处理器。提出正负图像组合编码方法，一步实现了通常需要三步的数学形态学击中击不中变换，提高了识别速度。改进传统的识别判据，改善了识别效果。采用一个液晶投影板同时显示待识别图像和参考图像，简化了结构。给出了实验结果。     

An ultrasonic signal processor for use in underwater acoustics

An ultrasonic signal processor is described which analyses information from conventional echo sounders fitted to small craft. Although an inexpensive accessory, it includes a number of novel features of value both to hydrographers and fishermen.The features include a high level of quantitative bottom discrimination, a wide dynamic range of fish abundance measurement with fine resolution (including modes for bottom trawling and net ‘flying’), the ability to detect fish close to the sea bottom, and the provision of audible warning systems. One of the features of the device is that while exploiting original scientific approaches, it permits these to be used in such a way as to augment, confirm and extend the professional experience of the individual fisherman.     

A near-infrared zero-order achromatic retarder

Phase retarders normally show strong wavelength dependence. Achromatic retarders which exhibit nearly identical characteristics over a wide wavelength spectrum is used in polychromatic light. The present investigation deals with a technique to design and study the characteristics of an achromatic combination of birefringent plates in 800–2000 nm range. The retarder has been designed using calcite, crystalline quartz and ADP. The thicknesses of the plates are 19.38 μm, 446.14 μm and 12.57 μm respectively. The new arrangement of three birefringent plates proposed has the promise of producing a zero-order quarter wave achromatic combination with fairly good accuracy.     

Design of liquid-glass achromatic zoom lens

Optical liquids are ideal materials for designing apochromatic lens due to their lower refractive index and higher Abbe numbers than those of the ordinary optical glasses. Based on the Buchdahl dispersion formula, the dispersion coefficient diagram of liquids and glasses is established. The liquid-glass combination lens(LGCL) with small secondary spectrum is obtained by calculating the combination structure with low dispersion liquid and glasses. The initial optical structure of the liquid-glass apochromatic lens(LGAL) can be obtained by replacing two glass lenses in an initial optical system with the LGCL. Using the multi-configuration optimization of ZEMAX, the liquid-glass achromatic zoom lens (LGAZL) can be designed by optimizing the LGAL. The LGAZL has an objective field of view ?63 mm–?57 mm, an image field of view 8 mm, a working distance 240 mm and the zoom range of focal length 75–85 mm. The chromatic aberration and the secondary spectrum of the LGAZL are all less than 3 μm in the whole zoom range.     

Nonuniform self-imaging of achromatic Talbot lithography

Achromatic Talbot lithography(ATL) with high resolution has been demonstrated to be an excellent technique for large area periodic nano-fabrication. In this work, the uniformity of pattern distribution in ATL was studied in detail. Two ATL transmission masks with ~50% duty cycle in a square lattice were illuminated by a spatial coherent broadband extreme ultraviolet beam with a relative bandwidth of 2.38%. Nonuniform dot size distribution was observed by experiments and finite-difference time-domain simulations. The sum of the two kinds of diffraction patterns, with different lattice directions(45° rotated) and different intensity distributions,results in the final nonuniform pattern distribution.     

Image formation with an achromatic interferometer

The imaging characteristics of an achromatic interferometer employing diffraction gratings are described.     

合成狭缝彩虹消色象全息术的研究

本文介绍一种二次曝光合成狭缝彩虹消色象全息术,详细地分析了点源全息图的结构、消色象的分辨率和景深.     

Numerical simulation of achromatic deflecting systems

A deflecting system formed by two parallel-plate capacitors on opposite sides of an optoelectronic element that alters the energy of a beam of charged particles, is calculated numerically. The conditions for correcting the chromatic beam spreading in the plane of the target are found. Good agreement with the results of an approximate analytical calculation is demonstrated. Zh. Tekh. Fiz. 67, 86–88 (December 1997)     

An adaptive moving mesh method for two-dimensional ideal magnetohydrodynamics

This paper presents an adaptive moving mesh algorithm for two-dimensional (2D) ideal magnetohydrodynamics (MHD) that utilizes a staggered constrained transport technique to keep the magnetic field divergence-free. The algorithm consists of two independent parts: MHD evolution and mesh-redistribution. The first part is a high-resolution, divergence-free, shock-capturing scheme on a fixed quadrangular mesh, while the second part is an iterative procedure. In each iteration, mesh points are first redistributed, and then a conservative-interpolation formula is used to calculate the remapped cell-averages of the mass, momentum, and total energy on the resulting new mesh; the magnetic potential is remapped to the new mesh in a non-conservative way and is reconstructed to give a divergence-free magnetic field on the new mesh. Several numerical examples are given to demonstrate that the proposed method can achieve high numerical accuracy, track and resolve strong shock waves in ideal MHD problems, and preserve divergence-free property of the magnetic field. Numerical examples include the smooth Alfvén wave problem, 2D and 2.5D shock tube problems, two rotor problems, the stringent blast problem, and the cloud–shock interaction problem.     

Ellipsometry with fourier transform spectrometer: An application to TaSi2 films

Summary Ellipsometric measurements on TaSi₂ polycrystalline films are presented in this paper. The optical functions are directly obtained in the wavenumber range from 400 to 3000 cm⁻¹ using an infrared ellipsometer coupled with a Fourier transform spectrometer. The analysis of the results provides the spectral range where the infrared response has a Drude-like behaviour. Finally, the optical resistivity at zero frequency is evaluated from the Drude parameters.