Showing papers on "Angular aperture published in 1994"

Aperture guiding in quasi-three-level lasers

Abstract: Aperture guiding, as opposed to thermal waveguiding, is shown to be the dominant mechanism for cavity mode stabilization in a quasi-three-level Yb:YAG laser in a flat-flat resonator. Excellent agreement is obtained between the experimental and modeled spot sizes in this laser when aperture guiding is included in the model. The models show that the spot size is insensitive to the exact form of the dependence of the transmission of the aperture on the transverse dimension. This finding is expected to affect other quasi-three-level lasers.

Characterization of resolution and uniqueness in crosswell direct‐arrival traveltime tomography using the Fourier projection slice theorem

Abstract: The process of acquiring a crosswell seismic direct‐arrival traveltime data set can be approximated by a series of truncated plane‐wave projections through an interwell slowness field. Using this approximation, the resolution and uniqueness of crosswell direct‐arrival traveltime tomograms can be characterized by invoking the Fourier projection slice theorem, which states that a plane‐wave projection through an object constitutes a slice of the object’s spatial spectrum. The limited vertical aperture of a crosswell survey introduces a small amount of nonuniqueness into the reconstructed tomogram by truncating the plane‐wave projection. By contrast, the limitations on angular aperture have a significant effect on resolution. The reconstructed tomogram is smeared primarily along the limiting projection angles, with the amount of smearing dependent upon the well spacing and the angular aperture. The amount of smearing was found to be inversely proportional to tan Δϕ, where Δϕ is the angular aperture illuminat...

Single aperture confocal imaging system

Abstract: A confocal scanning imaging system utilizes only one aperture for both the incident light from the light source and return light from the object To improve its performance, the aperture plate is tilted with respect to the incident light path, the surfaces are coated with anti-reflection coating, the surfaces are optically flat, and the size of the aperture is designed to act as a one-way spatial filter Other devices may be strategically placed to minimize the negative effects from scattered light

Superior resolution laser using bessel transform optical filter

Abstract: A fraction of the theoretical spot size in a lens system is obtained by applying a filter consisting of a variable pitch circular grating, in front of the focus lens. The focal point Image of a lens is a spot called an Airy disk. The diameter of the Airy disk is proportional to (wavelength)/(Numerical Aperture). Numerical aperture is equal to (1/2 of the diameter of the lens)/(focal length). This is the theoretical limit of spot size. Using a Bessel Transform, modified circular grating, filter the resulting first and higher order diffraction images lie on the optical axis and interfere resulting in a small beam spot at the focus surrounded by interference bands, producing a narrowed zero order beam for projection in optical and infrared applications.

Simulation of effects of phase and amplitude coatings on the lens aperture with polarization masks

Abstract: It is well known that circular symmetric phase and amplitude coatings on the lens aperture modify the imaging qualities of a lens. The present paper shows that the effects of such phase and amplitude coatings on the imaging properties of a lens can be achieved by using suitably oriented polarization masks on the lens aperture. The fact that the response of such a system can be continuously varied by changing the orientation of the polarizing devices included in the system lends it a versatility unobtainable by the use of conventional phase and amplitude coatings on the lens aperture.

Narrow linewidth BBO optical parametric oscillator utilizing extraordinary resonance

Abstract: Optical parametric oscillators using non-linear crystals cut for the type I interaction have an extraordinary pump beam which generates ordinary signal and idler beams. The use of an optical element to rotate the signal beam before sending this signal beam to a grating element allows for the grating element to have its dispersion plane oriented coplanar with the extraordinary crystal plane of the non-linear crystal. In this manner, for non-linear crystals which have relatively narrow acceptance angles, such as BBO crystals, the reduction in angular aperture of the parametric gain in the extraordinary plane will produce a reduction in the linewidth of the produced output. The grating translates the angular variations into variations in wavelength. If no rotator was used in the optical parametric oscillator, then in order to get the maximum efficiency out of the grating, the dispersion plane of the grating should be orthogonal to the extraordinary plane of the crystal, and therefore the narrow angular acceptance of the crystal would not result in a narrow output linewidth.

Inverted telephoto wide-aperture wide-field infrared lens system

Abstract: Design forms are disclosed for wide-field infrared imaging systems characterized by a large ratio of entrance aperture to focal length, where the limiting aperture stop is located in the converging image space.

Integrated optical-disk pickup that uses a focusing grating coupler with a high numerical aperture

Abstract: An integrated optical-disk pickup that uses a focusing grating coupler with a numerical aperture of 0.45 (a focal length of 1.0 mm and an aperture of 1.0 mm × 0.8 mm) was developed, and the readout signal on an International Standards Organization (ISO) -formatted 90-mm optical disk was detected by the pickup. The signal-amplitude ratio of the minimum-limit data pattern to the maximum was 0.53 on the innermost track. It meets the requirement on the signal resolution for optical-disk storage devices.

Analysis of active surface reflector antenna for a large millimeter wave radio telescope

Abstract: The authors analyze the effects of imperfect segment alignment on the aperture efficiency of a large millimeter telescope. A 50 meter diameter instrument of this type specified to operate to wavelengths as short as 1 mm is being designed with an actively controlled main surface. By simulating the performance of the control system, they generate samples of tilt and piston errors for the segments from which the antenna radiation patterns and aperture efficiencies are calculated. They make a comparison of these results with models of antenna tolerance theory developed by Ruze (1966), which relate the aperture efficiency to the RMS phase error. They find that Ruze's formulas have a different range of validity when the aperture RMS phase error, rather than the RMS surface error, is used as a parameter. When appreciable tilt errors are present in large segmented antennas, the aperture RMS phase error tends to a constant value, independent of the aperture illumination and of the shape of the segments. They conclude that the antenna RMS surface error is a better tracer of the aperture efficiency than is the aperture RMS phase error when Ruze's formula is used. They find that this well-known expression stands as a lower limit to the performance of large segmented reflector antennas. >

Objective lens for an optical disk drive

Abstract: An optical lens for an optical disk drive suppresses a chromatic aberration to a sufficiently small level and attain a numerical aperture of as large as 0.55. It comprises a biconvex positive lens and a meniscus negative lens arranged in this order as viewed toward an optical disk to form a two-piece cemented lens system. The cementing surface is spherical and other surfaces are aspherical. The lenses meet the conditions of: (1) ν 1 >70 (2) n 1 >1.55 (3) ν 1 -ν 2 >45 (4) 1.1<{-r 2 /(f·NA)}<1.5 where ν 1 is an Abbe's number of positive lens, ν 2 is an Abbe's number of the negative lens, n 1 is a refractive index on a d line of the positive lens, r 2 is a radius of curvature of the cementing surface, f is a combined focal distance of an entire system and NA is a numerical aperture of the entire system.

Equivalent currents for an aperture in an impedance surface

Abstract: Expressions of equivalent magnetic and electric currents for an aperture in an impedance surface is derived in a self-consistent manner. Each equivalent current consists of the combination of the tangential electric and magnetic fields in the aperture, and is placed in front of the original aperture where the surface is extended to close the aperture. The result is particularly useful for problems involving apertures in an impedance ground plane. >

Camera having an aperture controllable shutter

Abstract: A camera provided with an aperture controllable shutter capable of determining exposure by varying aperture movement, and a photographic lens capable of varying focal length. In accordance with the focal length of the photographic lens, an aperture size or an aperture characteristic of the aperture controllable shutter is determined. A diaphragm of the aperture controllable shutter is driven based on the determined aperture size, aperture characteristic and object brightness.

Large aperture medium telephoto lens system

Abstract: The lens system includes, in order from an object side, a 1-st lens unit having a positive refractive power which has at least two positive lens elements and a negative lens element positioned on an image side of said positive lens elements, a 2-nd lens unit having a positive refractive power and a 3-rd lens unit having a positive refractive power. During focusing, both 1-st and 3-rd lens units are fixed, whereas the 2-nd lens unit is movable along an optical axis. The lens system satisfies at least one of the conditions 1.8

Method of manufacturing a opto-electronic component with narrow aperture angle

Abstract: The invention relates to an opto-electronic component having a narrow aperture angle. The conventional design of components transmitting radiation or reacting to radiation and concentrating that radiation with the aid of lenses results, on account of the increasing distance between the lens and the semiconductor chip, in increasing component dimensions in the radiating or detecting direction with an increasingly narrow aperture angle. In accordance with the invention, a parabolic or approximately parabolic reflector is provided that is connected to a support strip supporting the semiconductor chip such that the latter is as close as possible to the focal point of the parabolic or approximately parabolic surface of the reflector. The reflector is preferably connected to the support strip by engaging elements and surrounded by a housing.

Optical quality and temperature profile of a spinning pipe gas lens

Abstract: A spatially resolved temperature measurement in a spinning pipe gas lens of aperture 2.25 cm and length 1 m, is presented. Ray tracing through the measured refractive index profile was performed. We show that by reducing the optical aperture of the lens (to 1 cm), an angular resolution of twice the diffraction limited is obtainable.

High-aperture raster holography for particle imaging.

Abstract: A novel approach to in-line particle holography is described, and its superiority is experimentally demonstrated. During recording, a raster diffuser is used to increase the effective angular aperture of particle scattering, and a raster screen is placed in front of hologram to mask the unscattered diffuse light. In reconstruction, a new type of spatial filter passes only the spherical waves from the interrogation region, effectively blocking the reconstruction beam, separating the real and virtual images, and suppressing the strong forward scattering. This new scheme provides particle images with higher contrast, reduced speckle noise, and a smaller depth of focus than conventional in-line holography.

Wide angular aperture lithium niobate acousto-optic Bragg cells

Abstract: A new design for a wide angular aperture Lithium Niobate acousto-optic Bragg cell is proposed. Parallel tangents, beam steering, and an acousto-optic interaction in a rotated 60 degree(s)-YZ plane are used simultaneously, which enhances the product of acceptance angle, bandwidth, and diffraction efficiency to be larger than that of isotropic acousto-optic Bragg cells by more than one order of magnitude. The analysis and optimum design procedure for acoustic beam steering in birefringent acousto-optic diffraction with the parallel tangents condition fulfilled is established and is essential for obtaining the maximum value of the above mentioned product. The acousto-optic interaction in the rotated YZ plane is analyzed and is important to obtain high diffraction efficiency for most cases where the parallel tangents condition is used. The optimal design of a wide angular aperture Lithium Niobate device working at 514.5 nm and with a center frequency of 150 MHz is carried out and is being fabricated.

Large aperture retrofocus lens

Abstract: A large aperture retrofocus lens system is composed of first to sixth lenses arranged in this order from the object side. The first lens has a positive refracting power, the second lens has a negative refracting power, the third lens which is a meniscus lens concave toward the object side, the fourth lens has a negative refracting power, the fifth lens has a positive refracting power and the sixth lens has a positive refracting power.

Acousto-optic modulator with wide bandwidth and large angular aperture

Abstract: A new type of acousto-optic (AO) modulator with enhanced performance is described. By using phased array transducers in a birefringent AO cell, it is possible to simultaneously satisfy the tangential and noncritical phase matching conditions and achieve both large bandwidth and angular aperture. The new design is optimum for modulators and low resolution deflectors with the important advantage of fast input optics.

Method and apparatus for concentrating and combining the energy of asymmetric diode laser beams

Abstract: Methods and apparatus are disclosed for concentrating the energy of a laser diode beam by imaging a first numerical aperture of the beam in one beam plane to a reduced numerical aperture at a focal plane, and by guiding the beam between reflective boundaries to maintain the value of a lesser second numerical aperture in another beam plane at the focal plane. The reduced numerical aperture in the first plane optimally matches the second numerical aperture in the second plane so that the energy can be received into the entrance end of an optical fiber whose numerical aperture also matches the second numerical aperture. The area of this fiber preferably matches that of the image at the focal plane. A coupler that guides the beam to its focal plane preferably utilizes an imaging element, e.g., a cylindrical lens or a cylindrical elliptical mirror, and a pair of spaced reflective walls. The exit ends of a plurality of fibers that are illuminated by respective beams can be closely packed into any desired pattern which can be fractionally magnified by a relay lens into a very concentrated energy pattern. If desired, this final image may be fed into a single optical fiber for passage through remote or convoluted optical paths.

Optical sensor for detecting indicatrices

Abstract: The sensor contains a special lens for deflecting a beam emitted from a point on the axis of symmetry in a spatial angle of about 2 pi into an axially parallel beam. The lens consists of smooth surfaces using both refraction and reflection for beam deflection and has different focal lengths for different emission angular regions. The lens is used in combination with a suitable input coupling lens for simultaneous top illumination of a specimen and to make a reflection indicatrix measurable. The aperture errors for both detection regions are reduced, e.g. by using a parabolic reflective surface (PA) and making the corresp. input surface (KZ) concentric with the emission point.

Compact wide-angle variable focal length lens system

Abstract: A wide-angle variable focal length lens system comprising a first lens unit which is to be kept stationary for varying a focal length of the variable focal lens system and composed of a single positive lens component, a second lens unit which comprises at least one positive lens component and has a negative refractive power as a whole, a stop, and a third lens unit having a positive refractive power; and configured so as to perform variation of a focal length of the lens system and adjustment of an image location by moving the second lens unit and the third lens unit along an optical axis in directions which are opposite to each other. This variable focal length lens system has a field angle of 64° to 74° at a wide position thereof, a variable focal length ratio of 3 to 3.3 and an F number on the order of 2, and comprises a small number of lens components.

In-vitro study of a computed ultrasound imaging method

Abstract: In the present computed ultrasound holography method a target is scanned with a wide-angle beam in a monostatic manner. Numerical image focusing takes place in the spatial frequency domain using efficient FFT-based algorithms. The beam is formed using 9 elements of a 3.5 MHz phased array. This results in a -12 dB angular aperture of 30 degrees when Blackman-Harris window was chosen as the weighing function for aperture apodization. The side lobe level of the beam could be depressed to -50 dB. The -6 dB spatial resolution was about 1 mm and uniform in a large depth range. By adopting an interpolation scheme the side-lobe level of the point-spread-function could be reduced to 40 dB. The enhanced image quality is demonstrated with in-vitro images of a liver-mimicking phantom and a fresh liver sample

An extension of the physical theory of diffraction concept for aperture radiation problems

Abstract: A correction to the Kirchhoff-Huygens approximation in the format of a diffraction coefficient is derived for an aperture terminated by a half plane. As in the physical theory of diffraction (PTD), this is achieved by considering the end point contribution to the aperture integral. It is seen that when the aperture is taken as conformal with the surface of the half plane, the conventional PTD result is obtained.

Super-resolution by focal plane immersion

Abstract: Diffraction patterns in a focal region are governed by immersing the focal region in dielectric medium having an index of refraction higher than one. The pattern of the focal region is made small by causing the focal region to be immersed in a body having an index of refraction greater than 1. The resulting diffraction pattern sensed appropriately in the focal region is independent of traditional aperture limitations in resolving power. Microwave pictures are taken at the same resolution as optical pictures using the same aperture size when an appropriate dielectric immersion material is provided.

Large angular aperture acousto-optic modulator

Abstract: This paper presents the theoretical analysis on a new type of AO modulator. The modulator achieves large modulation bandwidth and input angular aperture by simultaneously satisfying tangential phase matching and noncritical phase matching. A TeO2 modulator was designed that could provide an order of magnitude increase of the input angular aperture