Showing papers on "Angular aperture published in 1981"

Aperture Antennas and Diffraction Theory

Abstract: Chapter 1: Introduction Chapter 2: Plane waves from apertures Chapter 3: Fourier transform representation of aperture patterns Chapter 4: Near-field radiation patterns Chapter 5: Aperture gain Chapter 6: Applications of aperture theory to antennas Chapter 7: Diffraction by conductors with sharp edges Chapter 8: Geometrical theory of diffraction by edges Chapter 9: Applications of geometrical diffraction theory to antennas Appendixes

Diffraction of a gaussian beam through a finite aperture lens and the resulting heterodyne efficiency

Abstract: The diffraction field of a Gaussian beam through a finite aperture lens is investigated. The field distributions at the position where the field is most focused are shown and compared with those obtained by an infinite aperture lens. The results are applied to an optical heterodyne detection system with Gaussian fields, and the optimum conditions that maximize the heterodyne efficiency are obtained numerically.

Energy spreading in the hydrogen field ionization source

Abstract: The application of field ionization as a tool for routine submicron fabrication will depend critically upon the characteristics of the source; the angular intensity and the energy spread of the ions. The chromatic aberration coefficient of the ion optical system, the angular aperture, and the energy spread combine to set the limit of spot size and current density for very‐high‐resolution probes with sources of energy widths even as low as 1 eV. It is known that the various molecular species produced by hydrogen field ionization are indentifiable by the energy distribution, and because the mass of the ion will determine the particle range in resists at any given energy, energy measurements carry further importance in the development of the probe‐forming system. In order to characterize the source‐energy widths and mass species as a function of beam current, angular intensity, and surface characteristics of the emitter tip, we have designed and operated a unitized, positionable intermediate image filter len...

Wide angle projection system

Abstract: A projection system that is particularly suited for simulating aircraft flight includes a large dome and a projector and optical system that are located outside of the dome. The dome has a diffuse reflective surface that is presented inwardly. The projector produces a pattern of light which is redirected by the optical system such that it passes through an aperture in the dome, and is cast upon a wide area of the diffuse reflective surface as an image of a scene, particularly a scene that one might encounter from the cockpit of an aircraft. The optical system includes a concave mirror that is presented toward the aperture, a wide angle lens that is along the axis of the mirror, and a system of lens and folding mirrors for transmitting the light from the projector to the wide angle lens. The wide angle lens is located such that its pupil upon being reflected from the concave mirror reforms or comes into focus at the aperture in the dome. Thus, the light upon diverging from the wide angle lens reflects from the concave mirror and concentrates at the aperture through which it passes, diverging beyond the aperture to come into focus on the diffuse reflective surface, where it forms an image of the scene developed at the projector.

Curved reflector with adjustable focal length

Abstract: A curved reflector (10) of electro-magnetic radiation formed of an elastic, reflective membrane (14) which utilizes a partial vacuum to provide the curvature to the membrane (14) and an adjustablevalve (20) to vary such curvature, and therefore the focal length of the reflector (10). The valve (20) comprises a central aperture in the membrane (14) and a body adjustably mounted above the aperture with a flow restricting surface thereon which overlies the aperture.

Method of multiplexing transmission chanels in a step-index optical fibre and device for carrying out the method

Abstract: An optical multiplexer wherein a plurality of channels are formed in a step index optical fiber by groups of light rays which propagate along the fibre by consecutive total reflections at the core/cladding interface. The rays are grouped depending on their angle with the fibre axis so that for each channel, at any point of the fibre, the rays of a given group are situated between two cones whose common apex is formed by that point and which are rotationally symmetrical about a common axis parallel to the fibre axis. The cones define the portion of the angular aperture relating to each channel. The aperture portions relating to all the channels are moreover juxtaposed. A multi-axial optical system directs each of a plurality of light signals along a region defined by the cones so as to inject the light signal into the aperture portion of the associated channel for each channel at the fibre input and reception means which are specific of the aperture portion of said channel at the output.

Zone focusing optical system

Abstract: A zone focusing lens system is provided for use as a photographic camera objective. In the system, a fixed positive meniscus is placed ahead of the system aperture stop and is provided with an aspheric surface that is structured primarily to correct for off-axis aberrations. A lens disk having a plurality of different meniscus lens elements is located so that each of its elements can be selectively rotated into alignment proximate the system aperture stop to provide system focal lengths appropriate for sharply focusing objects located within different distance ranges. Each of the lens disk elements is provided with an aspheric surface that is structured primarily to reduce spherical aberrations.

Wide aperture objective lens

Abstract: An objective lens comprising five lens elements and intended for use in an optical recording system wherein a laser beam is focused onto a recording surface located beneath a plastic layer over the disc. The disclosed lens has a relatively large numeric aperture of 0.75, but has a relatively large working distance between the lens and the disc and a relatively low total mass, to facilitate rapid movement of the lens. In addition, the lens is color corrected to accommodate a range of spectral frequencies present in the laser beam.

Microscope optical system

Abstract: PURPOSE:To observe a more detailed structure of a phase substance, by using an optical control member containing a transmittance lowering member and a phase converting member to a linear part conjugate with a linear aperture part of a diaphragm member. CONSTITUTION:A diaphragm member 2 having a linear aperture member 2a is set on the focal plane at the incident light side of a condenser lens 1. The luminous flux supplied from the aperture part 2a which substantially functions as a light source is fed on a sample surface 3 through the lens 1. An image P' of a sample P is formed on an image surface 5 through an objective lens 4. An optical control member 6 provided on the focal plane of the output light side of the lens 4 contains an absorption/phase plate 6a at a linear part which is conjugate with the part 2a of the member 2 in terms of the lenses 1 and 4a. The diffracted light caused by a sample P is the oblique illumination beam which is supplied from only a single direction. As a result, a halo phenomenon which is peculiar to a phase difference type microscope never occurs to ensure the stereoscopic observation.

Large relative aperture objective lens

Abstract: An objective lens of large relative aperture includes three lens components of positive power arranged to be focused by moving the first and third components in unison forwardly, along with forward movement of the second component by a smaller amount than the movement of the first and third components when focusing down to shorter object distances. Accordingly, aberrations are well corrected throughout an extended range of image magnification.

Radiation from reflector antennas: Exact aperture and aperture‐like approaches

Abstract: A new computational approach is presented, which allows fast analysis of radiation from reflector antennas. The basic idea is the Fourier transform (FT) relationship between far-field and aperture distributions. Accordingly, the far field can be exactly reconstructed from the knowledge of spatial samples at angular rate ka sin θ cosϕ = n π ka sin θ sin ϕ = m π, where a is the aperture radius (Shannon-Whittaker theorem applied at Nyquist rate). The conclusion is that the aperture far field can be sampled at approximately one point per lobe. The finite reflector curvature introduces an extra term in the radiation integral which modifies the (finite) aperture/far-field FT relationship. There are two ways to overcome this difficulty: (1) consider an infinite aperture, thereby saving the FT relationship, but losing the spatially band-limited property and (2) reformulate the Shannon-Whittaker theorem in such a way as to take into account the extra (curvature) term. The first approach requires truncation of the infinite aperture to an assigned degree of approximation in the far-field computation. This states an equivalence between the field radiated by the reflector and the field radiated by an equivalent aperture of larger radius. Accordingly, the far field can still be reconstructed using the field radiated by the reflector, sampled at a higher rate (slightly higher for large dishes). These samples can be computed using physical optics or asymptotic techniques, whichever is appropriate. The second approach is based on a new sampling representation, which explicitly takes into account the extra term in the radiation integral. For a quadratic type of term, i.e., for parabolic reflectors, the sampling functions are the complementary error functions, and the far field can be exactly reconstructed in terms of the far field of an equivalent aperture. These samples can be computed using the fast Fourier transform, therefore further gaining in time saving. Computations showing the excellent performances of the two methods have been made, indicating the significant advantages provided in reflector antenna analysis.

Large relative aperture objective

Abstract: An objective lens of large relative aperture comprising, from front to rear, a first lens component of positive power, a second lens component of positive power and a third lens component of negative power, the first and third lens components being moved forward as a unit, while the second lens component is simultaneously moved forward by a smaller amount than that of the movement of them to effect focusing from infinity to shorter object distances. The focal lengths of the first, second and third lens components, the calculations of the constituent lenses, and the glass materials of which the lenses are made up are properly chosen so as to achieve a high grade imaging performance throughout a focusing range from infinity to very short object distances.

Camera lens system with long back focal distance and large aperture ratio

Abstract: A camera lens system is disclosed having a long back focal distance and a large aperture ratio. This enables the camera system to sufficiently correct for various aberrations including the spherical aberration of colors of the camera lens system.

Electromagnetic coupling between apertures and biological structures

Abstract: The coupling between a radiating aperture and a biological body standing in its near field region is analyzed, with particular reference to the evaluation of (1) em field distribution inside the biological body, including, in particular, the hot spots at the interface between two different biological media and (2) the effects of the body upon the aperture radiation characteristics (total radiated power and aperture transmission cross sections). The solution is obtained by applying the moment method technique to the aperture, once the em field distribution on the aperture has been approximated by a set of triangular functions and the biological body has been subdivided into homogeneous cubes. The numerical program has been written for use on a desk top computer and partitioned into subprograms in order to minimize the central memory requirements, by storing the partial results on a floppy disk. As an example the coupling between a λ/2 × λ/20 aperture excited by a plane wave and a cylindrical biological body is examined.

Aperture structure in zoom lens

Abstract: A separate set of aperture blades is provided for varying the maximum full aperture of a zoom lens as its magnification is changed. The second set of aperture blades are pivotally mounted to a support plate which also rotatably supports the conventional aperture blades.

Current distribution in shaped e-beams

Abstract: The current distribution in electron beams shaped by using either Kohler or critical illumination of apertures has been determined experimentally. The experimental technique is to scan a square image across sharp edges of a Faraday cage aperture while the first and second differentials of the current are displayed on an oscilloscope. The measurements show that the type of illumination is not an important factor in determining the ultimate edge sharpness. All measurements were made with 20‐kV accelerating voltage and it was found that for a square of side 3.5 μm imaged at an angular aperture 3.7 mrad the current density edge deteriorated to about 0.7 μ at 3 μA for both types of illumination. Results of imaging a menu of variable shapes in resist are used to demonstrate uniform current density distribution in the shaped beam.

Degrees of freedom of the field scattered by a rectangular prism in coherent illumination

Abstract: Some numerical results are reported and discussed concerning the number of degrees of freedom of the far field scattered by a cylindrical object illuminated by a coherent plane wave and observed through a pupil of finite angular aperture.

Asymmetries in the diffraction pattern of an asymmetrical aperture

Abstract: The two-dimensional diffraction pattern of a line aperture can exhibit certain asymmetries when the aperture excitation is asymmetric. The four lowest moments of the aperture distribution are responsible for the distortion near the focus. When the coordinate system is chosen so that the first moment is zero, the third central moment plays the dominant role. By coupling the angle and range coordinates, image artifacts, including shape distortion, can result.

Large aperture telephoto-lens

Abstract: The present invention relates to a large aperture telephoto-lens consisting of a positive front lens group including a positive lens, a negative lens and a positive lens in sequence and a rear lens group arranged distant from the front group on the optical axis and including a fixed negative sub-group and a movable negative sub-group for focusing, whereby the following relations are satisfied. 1.15¦R3¦ > ¦R2¦ > 1.04¦R3¦, R2 ¦R3¦ > 0.34f Hereby, v1, v2, v3 are Abbe's numbers of the lenses constituting the front lens group; n1, n2, n3 are refractive indices of the lenses constituting the front lens group; R2 is the radius of curvature of the image side surface of the object side positive lens in the front lens group; R3 is the radius of curvature of the object side surface of the negative lens in the front lens group; and f is the focal length of the whole system when an object at the infinite distance is in focus.