Showing papers on "Angular aperture published in 2015"

Orbital angular momentum mode-demultiplexing scheme with partial angular receiving aperture.

Abstract: For long distance orbital angular momentum (OAM) based transmission, the conventional whole beam receiving scheme encounters the difficulty of large aperture due to the divergence of OAM beams. We propose a novel partial receiving scheme, using a restricted angular aperture to receive and demultiplex multi-OAM-mode beams. The scheme is theoretically analyzed to show that a regularly spaced OAM mode set remain orthogonal and therefore can be de-multiplexed. Experiments have been carried out to verify the feasibility. This partial receiving scheme can serve as an effective method with both space and cost savings for the OAM communications. It is applicable to both free space OAM optical communications and radio frequency (RF) OAM communications.

Spherical aberration free liquid-filled tunable lens with variable thickness membrane

Abstract: We present an iterative design method for liquid-tunable aspherical lenses capable of diffraction-limited performance over a wide focal length range. The lenses are formed by a thin elastomer meniscus with a variable thickness profile engineered to deform into an ideal asphere under uniform pressure load. Compared to their more conventional counterparts, the proposed lenses significantly reduce spherical aberration over a larger portion of the aperture. The design procedure begins with the semi-analytical calculation of the meniscus thickness profile using large-deflection thin plate theory. This initial profile is then further optimized using coupled finite element analysis and ray-tracing simulations iteratively. We apply the developed method to design a tunable aspherical lens with 3 mm clear aperture and 8 mm optimum focal length, and numerically demonstrate the improvement in optical performance over conventional tunable-lenses over a focal length range from 6 mm to 12 mm. Using 80% of the clear aperture, the lens has better than λ/4 RMS surface error over the focal length range from 7.7 mm to 8.5 mm, corresponding to 10% tuning of focal length with diffraction-limited performance. The sources of potential fabrication errors in a practical implementation of such a lens are also analyzed in detail in terms of their influence on optical performance.

Effect of the angular aperture of medical ultrasound transducers on the parameters of nonlinear ultrasound field with shocks at the focus

Abstract: Certain modern applications of high-intensity focused ultrasound (HIFU) in medicine use the nonlinear effect of shock front formation in the focal waveform. However, an important problem remains unsolved: determination of transducer parameters that provide the given pressure levels of the shock wave field at the focus required for a specific application. In this paper, simulations based on the Khokhlov-Zabolotskaya equation are performed to test and confirm the hypothesis that angular aperture of the transducer is the main parameter that determines the characteristic amplitude of the shock front and corresponding values for the peak positive and negative pressures at the focus. A criterion for formation of a developed shock in the acoustic waveform, as well as a method for determining its amplitude is proposed. Quantitative dependences of the amplitude of the developed shock and the peak pressures in the wave profile on the angular aperture of the transducer are calculated. The effects of saturation and the range of changes of the shock waveform parameters at the focus are analyzed for a typical HIFU transducer.

Three-Dimensional Scattering Center Extraction Based on Wide Aperture Data at a Single Elevation

Abstract: A methodology to reconstruct the 3-D scattering center model from the data with wide azimuthal aperture at a single elevation, such as those collected in turntable or circular synthetic aperture radar configurations, is proposed in this paper. The wide azimuthal aperture is divided into overlapped subapertures, and the 2-D scattering centers are extracted in each subaperture. These local scattering centers are rotated and mapped into the ground plane in the target coordinate system, where they are associated according to their location and amplitude consistency. Three-dimensional position of the scatterer is then estimated from the location variation of the 2-D points at different azimuths. The theoretical performance of the position estimator is analyzed, which reveals how the scatterers' azimuthal directivity and persistency affect the precision of the position estimates. The reconstructed model consisted of scattering centers described by their 3-D positions and scattering coefficient profiles at the specific depression angle. Examples using both point scatterers and computer-aided design models not only verify the validity of the methodology but also manifest the applicability of the reconstructed model in scattering analysis, data regeneration, and elevation extrapolation.

Stitching interferometry for cylindrical optics with large angular aperture

Abstract: Stitching interferometry is an attractive method for measuring optics with large apertures. However, existing stitching algorithms are not suitable for measuring cylindrical optics, because the misalignment aberrations in cylindrical interferometry are more complicated than those in plane, spherical and aspherical measurements. This paper presents a stitching algorithm for measuring cylindrical optics with large angular apertures. With it, we use five aberrations (i.e. piston, tilt, tip, defocus and twist) to describe the possible misalignments of the tested cylindrical surface and to build the cylindrical stitching model. Using this model allows us to calculate the relative misalignment aberrations of subapertures from their overlapped areas, so that the full aperture map of a cylindrical surface is obtained by compensating for these misalignment aberrations. In experiment, a cylindrical lens with an angular aperture over 150° is measured, thus demonstrating the feasibility and validity of the proposed method.

Wide-angle imaging lens and imaging apparatus

Abstract: An imaging lens is composed of a first lens having a negative meniscus shape with a convex surface on the object side, a negative second lens, a positive third lens, an aperture stop, a negative fourth lens, and a positive fifth lens disposed in order from the object side. The fourth and the fifth lens are cemented with an interface which is convex on the object side and has an aspherical shape. If the radius of curvature is taken as R9 and the focal length of the entire system is taken as f, the imaging lens satisfies a conditional expression given below: 1.0< R 9/ f (1).

Adaptable operating frequency of a variable focal length lens in an adjustable magnification optical system

Abstract: An imaging system is provided for a precision machine vision inspection or metrology system. The imaging system optical path includes a variable magnification lens portion and a variable focal length lens portion. The variable magnification lens portion includes various magnification states (e.g., 0.5× to 100×, using interchangeable lenses, or the like.) The variable focal length lens portion (e.g., including a tunable acoustic gradient index of refraction (“TAG”) lens) is operated at different focal length scanning frequencies depending on the magnification state. A TAG lens operated in this manner provides a relatively consistent range of focus (e.g., corresponding to a number of depths of field) with various magnification lenses, without limiting the effective numerical aperture of the imaging system.

Fraunhofer diffraction of Laguerre-Gaussian beam caused by a dynamic superposed dual-triangular aperture

Abstract: We investigate the Fraunhofer diffraction of a Laguerre-Gaussian (LG) beam incident on a dynamic superposed dual-triangular aperture. The evolution of the diffraction pattern from this aperture is analyzed experimentally and theoretically. A special aperture, called the hex-star triangular aperture, demonstrates interesting diffraction patterns. Further, the diffraction properties of integer, half-integer, and fractional orders of topological charges at the Fraunhofer zone are studied by using the hex-star triangular aperture. This study can provide additional information to enhance the understanding of the diffraction properties of the LG beam transmitted through a complex aperture. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)

Flat-base broadband multibeam Luneburg lens for wide-angle scan

Abstract: In this paper, we present the design of a flat-base Luneburg type of lens antenna, designed for wide-angle scan. The antenna consists of a 11-layer lens, fed at its base by a array of waveguides. The lens is broadband and has a high aperture efficiency, only 1 dB below that of a reference aperture antenna with uniform amplitude and phase distributions. Its sidelobe level is –21 dB at boresight and –13 dB when the scan angle is . It shows good performance when compared to the flat Luneburg lens previously reported in the literature, in terms of gain, scan capability, as well as ease of fabrication. It is shown to have the capability of producing multiple beams simultaneously, multiple angle, scan capability. Two different methodologies have been used to design the feed array of waveguides for the lens. The first of these utilizes a conventional perfect electric conductor waveguide, while the second employs materials for the guided wave region that has a high permittivity at frequencies at which metals beco...

A new possibility for production of sub-picosecond x-ray pulses using a time dependent radio frequency orbit deflection

Abstract: It is shown that two radio frequency deflecting cavities with slightly different frequencies can be used to produce time-dependent orbit deflection to a few special electron bunches circulating in a synchrotron without affecting the majority of the electron bunches. These special bunches produce an x-ray pulse in which transverse position or angle, or both, are correlated with time. The x-ray pulse is then shortened, either with an asymmetrically cut crystal that acts as a pulse compressor, or with an angular aperture such as a narrow slit positioned downstream. The implementation of this technique creates a highly flexible environment for synchrotrons in which users of most beamlines will be able to easily select between the x-rays originated by the standard electron bunches and the short x-ray pulses originated by the special electron bunches carrying a time-dependent transverse correlation.

Modified x-ray polymer refractive cross lens with adiabatic contraction and its realization

Abstract: A refractive x-ray lens with reduced focal length, due to continuous reduction in the designed aperture over the length of the lens, is presented. The lens elements have refractive parabolic sidewalls like geometrical prisms, with a varying cross section over the length of the lens, in accordance with the x-ray propagation law. The focusing effect occurs directly in the lens due to the fact that the initial x-ray beam is directed toward the focal point, and due to the phase retardation caused by the refractive properties of the sidewall surfaces. An array of such adiabatic lens elements with different optical parameters, arranged in a number of rows, represented by polymer microstructures, has been produced using x-ray lithography. Preliminary testing of the lenses has resulted in a focal spot of 67 nm at a photon energy of 18.6 keV.

Intensity Distribution of the Finite Olver Beams through a Paraxial ABCD Optical System with an Aperture of Basis Annular Aperture

Abstract: Based on the Collins diffraction formula and by means of the expansion of a hard aperture function into a finite sum of complex Gaussian functions, two analytical approaches of the Finite Olver beams (FOBs) passing through a paraxial ABCD optical system with a circular annular aperture or a rectangular one are developed in this paper. The propagation properties of the FOBs through an unapertured ABCD optical system or through this last with a circular (or rectangular) aperture or a circular (or rectangular) black screen are deduced, from the main results, as particular cases. Also, the characteristics of Finite ordinary Airy beam passing through the all considered optical systems are derived here that correspond to zeroth-order of the FOBs. According to the predicted formulas, computer simulation examples are given to deepen the understanding of the characteristics of the FOBs passing through some optical systems of annular aperture basis.

Wide-angle lens system and imaging apparatus

Abstract: A wide-angle lens system includes a first lens group, an aperture stop, and a second lens group having positive optical power. The first lens group includes, at least, a first lens element that has a meniscus shape convex on the object side, and has negative optical power, a second lens element that has a meniscus shape convex on the object side, and has negative optical power, a third lens element that is concave on the image side and has negative optical power, and a posterior lens element. The second lens element is an aspherical lens, and the second lens element satisfies a conditional expression: 0.3<(R21−R22)/(R21+R22)<0.8 where R21 is a radius of paraxial curvature on the object side of the second lens element, and R22 is a radius of paraxial curvature on the image side of the second lens element.

High numerical aperture objective lens system

Abstract: An objective lens system having a high numerical aperture, a large working distance, and low optical aberrations over a wide spectral band of wavelengths is disclosed. The objective lens system includes a first lens group, a second lens group, and a third lens group. The first lens group includes first and second positive meniscus lenses that are positioned at a distance from each other along an optical axis of the objective lens system. The distance may be dependent on a focal length of the objective lens system. The second lens group includes first and second meniscus lenses and a bi-convex lens. The third lens group includes a bi-concave lens and a doublet lens.

Diffraction of a focused wave by an aperture: a new perspective

Abstract: A new approach for calculating the field in the focal region along lines through the focal point of a lens is presented. In particular, the method is applied to a circular aperture. It is also applied to other shaped apertures, including circular sectors or segments, such as a semicircular aperture or Hilbert mask, and to polygonal shapes. The diffracted field is calculated by a one-dimensional Fourier transform, and can be used for accurate calculation at observation points distant from the focus. The approach gives new insight to appreciating the asymptotic behavior of the diffracted field, and the existence of intensity zeros, for different aperture shapes.

Use of diverging apertures to minimize the edge scatter in passive scattering proton therapy

Abstract: The purpose of this study was to evaluate the use of diverging-cut aperture to minimize collimator contamination in proton therapy. Two sets of apertures with nondivergent and divergent edge were fabricated to produce a 10 cm × 10 cm field at the radiation isocenter of a single-room proton therapy unit. Transverse profiles were acquired in a scanning water tank with both aperture sets. Up to 9.5% extra dose was observed from aperture scattering near the field edges with the nondivergent aperture set at 2 cm above the water surface and remained 3.0% at depth of 10 cm. For the divergent set, the contamination was reduced to less than 3.5% and 1.3%, respectively. Our study demonstrated that scattering from apertures contaminated the dose distribution near the field edge at shallow depth. A diverging-cut aperture was capable of reducing the contamination and is recommended for use in passive scattering proton therapy, especially when critical organs are lateral and proximal to the target at shallow depth.

Layer Thickness Determination

Abstract: For determination of film thickness with a reflectometer, the incident light is usually perpendicular to the film. Often, however, measuring heads are used that keep the aperture of the optical fiber constant or even microscopes are used to increase the lateral resolution in film thickness determination. Analogous to a fixed angle of incidence α the thickness determination is influenced in both cases. In contrast to a fixed angle now all angles between 0° and the aperture angle αapt are present for a measuring head or a microscope objective. We demonstrate here, how the aperture of the measuring head affects the thickness determination and give a quantitative estimation of the influence by assigning an effective angle of incidence αeff to a measuring head with aperture angle αapt.

Fresnel diffraction of aperture with rough edge

Abstract: The Fresnel diffraction of an aperture with a rough edge is studied in this paper. Circular and elliptical apertures with sinusoidal and random edges are chosen as examples to investigate the influence of the aperture edge on the diffraction. The numerical calculation results indicate intuitively the variations of the transverse and longitude diffraction intensity distributions with the edge parameters of the aperture. The data files of aperture models are obtained through the numerical calculations, and the aperture samples are obtained with the help of a liquid crystal light modulator (LCLM). Thus, the practical experiments of the diffractions of apertures with rough edges are carried out. The measured results are consistent with the calculated ones. The approximate analytic expressions of the diffraction by the modified aperture are deduced on the basis of the Fresnel diffraction theory and the statistic optics, and the reasonable explanations for the influence of edge parameters on the diffraction are given through the theoretical analysis.

An imaging system in reflection mode using coherent diffraction imaging methods and using micro-pinhole and aperture system

Abstract: An apparatus and a method of imaging a reflective sample, in particular for patterned and blank DUV, EUV masks, includes making an optics system; exposing the mask to obtain an aerial image include tomographic image and developing an optical parameter of the optical system associated with the aerial image according to the micro-pinhole system using scanning coherent diffraction methods. Said apparatus comprises : a) a radiation source (10), such as an EUV source, a DUV source, a BEUV or an X-ray source, that can have a relevant low temporal or spatial coherence to emit a light beam (22); b) a first focusing element (12), such as a Fresnel plate or a toroidal mirror, in order to focus the emitted beam to the required extend; c) a mirror (16) that reflects the focused beam towards the sample (6) to be analyzed; the beam being directed at an angle of 2 to 25°, preferably at an angle of about 6°, towards the sample (6) as compared to the normal vector of the surface of the sample (6); d) a pinhole aperture plate (18) which allows with its first aperture (al) to focus and cut-off the beam diameter to the desired extent thereby forming also the beam to become more monochromatic as compared to the light beam (22) as originally emitted from the light source (10); e) a mechanism (17) to displace the sample (6) continuously or step-wise in a direction perpendicular to the normal vector of the sample surface to allow to analyze the sample (6) which reflects the light beam that has passed the first aperture (a1) of the pinhole aperture plate (18) disposed upstream of the sample (6) under the same angle of the incident light, such as 6° for example with reference to the preferred example mentioned above; f) said pinhole aperture plate (18) having a second aperture (a2) as transparent window allowing with its second aperture being disposed adjacent to the first aperture (a1) to limit the diameter of the beam reflected by the sample (6) thereby adjusting the diameter of the light beam; and g) a pixel detector (20) to analyze the reflected beam that has passed the second aperture (a2).

Large-Field X-ray Imaging at SPring-8 BL20B2

Abstract: The medium-length (215 m) bending-magnet beamline 20B2 is allocated to medical applications and various X-ray micro imaging techniques (e.g., angiography, computed tomography, phase contrast imaging and diffraction topography) [1]. The unique properties of BL20B2 are high spatial coherence (large coherent length) and its wide beam cross-section, which come from its long beam transport path and bending magnet light source. The horizontal angular aperture of BL20B2 is 1.5 mrad, as in all bending magnet beamlines at SPring-8. The horizontal beam width at the end station is larger than 300 mm for a 215 m beamline length.

Diffraction optical field of the Bessel beam through elliptical annular aperture

Abstract: Based on Fresnel diffraction theory and complex Gaussian function expansion of hard-edged aperture, the optical field formula of Bessel beam propagating through an elliptical annular aperture is derived, and the transverse intensity distribution of the beam is numerically simulated. The changes of the optical field and the propagation process of the diffracted beam behind the elliptical annular aperture are studied. In the experiment for the first time, a quasi non-diffracting beam is generated by an axicon and the patterns that are due to the beam diffraction by an elliptical annular aperture at different propagation distances are observed with a charge-coupled device camera. The theoretical analysis and experimental results both show that Bessel beam passing through an elliptical annular aperture can generate a hollow beam.

Wire-grid polarizer using galvanic growth technology: demonstration of a wide spectral and angular bandwidth component with high extinction ratio

Abstract: Functional demonstration of a wide band, wide angular width wire-grid polarizer has been made in the framework of a user project of the European project ACTMOST (Access To Micro-Optics Expertise, Services and Technologies). The polarization function relies on linear polarizers using the wire-grid polarizer principle by means of a metal grating of unusually large period, exhibiting a large extinction of the transmission of the TE polarization in the 850-nm wavelength range. This grating achieves a broadband and especially high angular aperture reflection with low loss and permits resorting to very low cost incoherent light sources for the transmitted TM polarization. This paper will describe the design, the modeling and optimization, as well as the complete technological process chain, that has been used, starting with the photoresist grating printing using phase-mask UV-based lithography to the uniform galvanic growth of a very shallow gold grating on transparent conductive layer deposited on a glass substrate. Transmission curves for both polarizations performed on the first demonstrators will be presented.

Retroreflector spherical satellite

Abstract: Specific features of spherical retroreflector arrays for high-precision laser ranging are considered, and errors in distance measurements are analyzed. A version of a glass retroreflector satellite with a submillimeter “target error” is proposed. Its corner cube reflectors are located in depressions to reduce the working angular aperture, and their faces have a dielectric interference coating.

Influence of aperture lens system on optical information processing

Abstract: Considered some aspects of the formation and propagation of optical wave beams in lens systems. Considered as an example the two-lens optical information processing system. Analysis of the two-lens optical circuit has been made with a systems approach perspective. As part of the radio-optical analogies had been applied certain provisions of the theory of dynamical systems to the spatial optical system. The lens system is represented as a simple series-connected optical elements with known spatial impulse response. General impulse response of such a system has been received, as well as consider some special cases of the impulse response. The question of the relationship between the parameters and the size of the input aperture lenses for undistorted transmission of the optical signal has been considered. Analysis of the energy loss resulting from the finite aperture of the lens. It's based on an assessment of the fraction of radiation that propagates beyond the lens. Analysis showed that the energy losses depend explicitly on the following parameters: radiation wavelength, distance between input aperture and lens, and ratio of the input aperture and lens aperture. With the computer help simulation the dependence of losses was shown on the above parameters.

Optical system having small perspective distortion and ultra-wide viewing angle

Abstract: An optical system, including, sequentially from an object side to an image side: a first lens; a second lens; a third lens; an aperture; a fourth lens; a fifth lens; a sixth lens; a seventh lens; an optical filter; and a photosensitive chip. The first lens is a meniscus aspherical lens. The second lens is a meniscus aspherical lens. The third lens is a biconvex aspherical lens. The fourth lens is a meniscus aspherical lens. The fifth lens is a meniscus spherical lens. The sixth lens is a meniscus spherical lens. The seventh lens is a biconvex aspherical lens.

Closed-form near-field expressions for electromagnetic scattering by an electrically small circular aperture on a conducting screen

Abstract: Closed-form expressions were derived for the near-zone scattered fields caused by an obliquely incident plane wave of arbitrary polarization on a sub-wavelength circular aperture on an infinite conducting screen with an infinitesimal thickness. The analysis is based on a quasi-static model of the governing fields in the aperture which was published in the mid 40’s by Bethe and improved by Bouwkamp a few years later by incorporating additional terms. Starting with first-order analytical expressions for the magnetic surface current density in the aperture, the scattering problem was formulated using the vector potential F→, the equivalence principle, and the image theory resulting in surface integrals over the aperture which involve the free-space Green’s function. Using valid approximations for the near-zone field formulation, closed-form analytical expressions were derived for the corresponding scattered fields along the axis of the aperture. Obtained results based on these closed-form expressions were co...

Ion optics of probe-forming systems on the base of magnetic quadrupole lenses with conical aperture

Abstract: This paper describes the performance of probe-forming systems based on a new type of magnetic quadrupole lens with a conical aperture (MQL CA) The main difference in the MQL CA from the conventional quadrupole lens with a cylindrical aperture is that the poles in it are not parallel to the lens axis and positioned at a certain angle The basic advantage of such a lens is that the conical angle of the aperture allows the profile of the longitudinal distribution of the main components of the quadrupole field to be changed It provides for the changing of the focal length value, displacement of the principal plane relative to the centre of the lens and aberration variations depending on the conical angle A theoretical study of the ion optics of the probe-forming systems consisting of a triplet MQLs CA was carried out A comparison of the systems with MQLs CA and conventional systems based on the magnetic quadrupole lens (MQL) with a cylindrical aperture shows the possibility of increasing the acceptance of the first due to using the new type of lens