Showing papers on "Lens (optics) published in 1986"

Scanning electron microscope

Abstract: PURPOSE:To remove influence due to a reflective electron, from a secondary electron image on a sample surface by applying negative voltage to a grid stretched at a small distance from the under surface of the object lens of a scanning electron microscope so as to cover the under surface. CONSTITUTION:A grid 8 is stretched at a small distance from the under surface of an object lens 3 in a scanning electron microscope along said under surface so as to cover other parts except a lens opening 4 and the negative voltage is applied to the object lens 3 set at the earth potential. The secondary electron emitted from the spots other than a sample surface 6 on account of the electron reflected from the sample 6 is blocked by a grid 8 and only the secondary electron from the sample 6 is made incident in a secondary electron detector 2. Therefore, the secondary electron image on the cathode-ray tube is defined to only the information from the sample surface and the S/N ratio of the electron microscope can be improved.

Opto-mechanical systems design

Abstract: THE OPTO-MECHANICAL DESIGN PROCESS Introduction Conceptualization Performance Specifications and Design Constraints Preliminary Design Design Analysis and Computer Modeling Error Budgets and Tolerances Experimental Modeling Finalizing the Design Design Reviews Manufacturing the Instrument Evaluating the End Product Documenting the Design References ENVIRONMENTAL INFLUENCES Introduction Parameters of Concern Environmental Testing of Optics References OPTO-MECHANICAL CHARACTERISTICS OF MATERIALS Introduction Materials for Refracting Optics Materials for Reflecting Optics Materials for Mechanical Components Adhesives Sealants Special Coatings for Opto-Mechanical Materials Techniques for Manufacturing Opto-Mechanical Parts References MOUNTING INDIVIDUAL LENSES Introduction Considerations of Centered Optics Cost Impacts of Fabrication Tolerances Lens Weight and Center of Gravity Location Mounting Individual Low-Precision Lenses Mountings for Lenses with Curved Rims Mountings Interfacing with Spherical Surfaces Elastomeric Mountings for Lenses Mounting Lenses on Flexures Alignment of the Individual Lens Mounting Plastic Lenses References MOUNTING MULTIPLE LENSES Introduction Multielement Spacing Considerations Examples of Lens Assemblies with No Moving Parts Examples of Lens Assemblies Containing Moving Parts Lathe Assembly Techniques Microscope Objectives Assemblies Using Plastic Parts Liquid Coupling of Lenses Catadioptric Assemblies Alignment of Multi-Lens Assemblies Alignment of Reflecting Telescope Systems References MOUNTING WINDOWS AND FILTERS Introduction Conventional Window Mounts Special Window Mounts Mounts for Shells and Domes Conformal Windows Filter Mounts Windows Subject to a Pressure Differential References DESIGNING AND MOUNTING PRISMS Introduction Geometric Relationships Designs for Typical Prisms Kinematic and Semikinematic Prism Mounting Principles Mounting Prisms by Clamping Mounting Prisms by Bonding Flexure Mounts for Prisms References DESIGN AND MOUNTING SMALL, NONMETALLIC MIRRORS, GRATINGS, AND PELLICLES Introduction General Considerations Semikinematic Mountings for Small Mirrors Mounting Mirrors by Bonding Flexure Mounts for Mirrors Multiple-Mirror Mounts Mountings for Gratings Pellicle Design and Mounting References LIGHTWEIGHT NONMETALLIC MIRROR DESIGN Introduction Material Considerations Core Cell Configurations Cast Ribbed Substrates Slotted-Strut and Fused Monolithic Substrates Frit-Bonded Substrates Low-Temperature Bonded Substrates Machined-Core Substrates Contoured-Back Solid Mirror Configurations Thin Face Sheet Mirror Configurations Scaling Relationships for Lightweight Mirrors References MOUNTING LARGE, HORIZONTAL-AXIS MIRRORS Introduction General Considerations of Gravity Effects V-Type Mounts Multipoint Edge Supports The Ideal Radial Mount Mercury Tube Mounts Strap and Roller-Chain Mounts Push-Pull Mounts Comparison of Dynamic Relaxation and Finite-Element Analysis Techniques References MOUNTING LARGE VERTICAL-AXIS MIRRORS Introduction Ring Mounts Air Bag (Bladder) Mounts Multiple-Point Supports Metrology Mounts References MOUNTING LARGE, VARIABLE-ORIENTATION MIRRORS Introduction Mechanical Flotation Mounts Hydraulic/Pneumatic Mounts Center-Mounted Mirrors Mounts for Double-Arch Mirrors Bipod Mirror Mounts Thin Face Sheet Mirror Mounts Mounts for Large Space-Borne Mirrors References DESIGN AND MOUNTING OF METALLIC MIRRORS Introduction General Considerations of Metal Mirrors Aluminum Mirrors Beryllium Mirrors Mirrors Made from Other Metals Mirrors with Foam and Metal Matrix Cores Plating of Metal Mirrors Single-Point Diamond Turning of Metal Mirrors Conventional Mountings for Metal Mirrors Integral Mountings for Metal Mirrors Flexure Mountings for Larger Metal Mirrors Interfacing Multiple SPDT Components to Facilitate Assembly and Alignment References OPTICAL INSTRUMENT STRUCTURAL DESIGN Introduction Rigid Housing Configurations Modular Design Principles and Examples A Structural Design for High Shock Loading Athermalized Structural Designs Geometries for Telescope Tube Structures References ANALYSIS OF THE OPTO-MECHANICAL DESIGN Introduction Failure Predictions for Optics Stress Generation at Opto-Mechanical Interfaces Parametric Comparisons of Annular Interface Types Bending Effects Due to Offset Annular Contacts Effects of Temperature Changes Effects of Temperature Gradients Stresses in Cemented and Bonded Optics Due to Temperature Changes Some Effects of Temperature Changes on Elastomerically Mounted Lenses References APPENDIX A: UNITS AND THEIR CONVERSION APPENDIX B: SUMMARY OF METHODS FOR TESTING OPTICAL COMPONENTS AND OPTICAL INSTRUMENTS UNDER ADVERSE ENVIRONMENTAL CONDITIONS APPENDIX C: HARDNESS OF MATERIALS APPENDIX D: GLOSSARY INDEX

Planar three-dimensional constrained lenses

Abstract: A new design for a beamforming lens is presented. Both faces are planar arrays of radiating elements interconnected by transmission lines whose length varies as a function of radius. While the front face elements are regularly spaced, the back face elements are displaced radially from their corresponding front face elements, the amount of displacement also being a function of radius. We show that such a lens is capable of forming low sidelobe beams over an angular sector 36 beamwidths across in all planes of \phi by switching between clusters of only seven feed elements. Because both faces are planar, construction of lightweight lenses for multibeam antennas should be feasible.

Focus detecting device

Abstract: A focus detecting device arranged to detect the focusing condition of an objective lens by projecting a light flux from a light source onto an object through the objective lens and by sensing the light flux after it is reflected from the object. The focus detecting device is provided with sensors which produce information necessary for detecting the focal point of the objective lens by sensing the light of the light source reflected by the object. Degradation of the device's detection accuracy due to the eccentrically mounted objective lens is prevented when these sensors are symmetrically arranged relative to a plane containing the optical axis of the objective lens.

Surgical device for implantation of a deformable intraocular lens

Abstract: The invention provides an improved intraocular lens structure comprising a deformable optical zone portion with prescribed memory characteristics and methods and devices for implantation of such lens in the eye. The unique optical zone portion of the lens can be deformed by compressing, rolling, folding, stretching, or can be deformed by a combination of these techniques to temporarily reduce the optical zone portion to a diameter of about 80% or less of the cross-sectional diameter of the optical zone portion in an unstressed state. After insertion into the eye, the optical zone portion returns to its original configuration, full size and fixed focal length. The inventive methods and devices for implantation permit insertion of the improved lens through a relatively small incision made in the ocular tissue, thereby providing a safer, more convenient surgical procedure and more comfortable fit for the eye.

Opto-mechanical systems design

Abstract: THE OPTO-MECHANICAL DESIGN PROCESS Introduction Conceptualization Performance Specifications and Design Constraints Preliminary Design Design Analysis and Computer Modeling Error Budgets and Tolerances Experimental Modeling Finalizing the Design Design Reviews Manufacturing the Instrument Evaluating the End Product Documenting the Design References ENVIRONMENTAL INFLUENCES Introduction Parameters of Concern Environmental Testing of Optics References OPTO-MECHANICAL CHARACTERISTICS OF MATERIALS Introduction Materials for Refracting Optics Materials for Reflecting Optics Materials for Mechanical Components Adhesives Sealants Special Coatings for Opto-Mechanical Materials Techniques for Manufacturing Opto-Mechanical Parts References MOUNTING INDIVIDUAL LENSES Introduction Considerations of Centered Optics Cost Impacts of Fabrication Tolerances Lens Weight and Center of Gravity Location Mounting Individual Low-Precision Lenses Mountings for Lenses with Curved Rims Mountings Interfacing with Spherical Surfaces Elastomeric Mountings for Lenses Mounting Lenses on Flexures Alignment of the Individual Lens Mounting Plastic Lenses References MOUNTING MULTIPLE LENSES Introduction Multielement Spacing Considerations Examples of Lens Assemblies with No Moving Parts Examples of Lens Assemblies Containing Moving Parts Lathe Assembly Techniques Microscope Objectives Assemblies Using Plastic Parts Liquid Coupling of Lenses Catadioptric Assemblies Alignment of Multi-Lens Assemblies Alignment of Reflecting Telescope Systems References MOUNTING WINDOWS AND FILTERS Introduction Conventional Window Mounts Special Window Mounts Mounts for Shells and Domes Conformal Windows Filter Mounts Windows Subject to a Pressure Differential References DESIGNING AND MOUNTING PRISMS Introduction Geometric Relationships Designs for Typical Prisms Kinematic and Semikinematic Prism Mounting Principles Mounting Prisms by Clamping Mounting Prisms by Bonding Flexure Mounts for Prisms References DESIGN AND MOUNTING SMALL, NONMETALLIC MIRRORS, GRATINGS, AND PELLICLES Introduction General Considerations Semikinematic Mountings for Small Mirrors Mounting Mirrors by Bonding Flexure Mounts for Mirrors Multiple-Mirror Mounts Mountings for Gratings Pellicle Design and Mounting References LIGHTWEIGHT NONMETALLIC MIRROR DESIGN Introduction Material Considerations Core Cell Configurations Cast Ribbed Substrates Slotted-Strut and Fused Monolithic Substrates Frit-Bonded Substrates Low-Temperature Bonded Substrates Machined-Core Substrates Contoured-Back Solid Mirror Configurations Thin Face Sheet Mirror Configurations Scaling Relationships for Lightweight Mirrors References MOUNTING LARGE, HORIZONTAL-AXIS MIRRORS Introduction General Considerations of Gravity Effects V-Type Mounts Multipoint Edge Supports The Ideal Radial Mount Mercury Tube Mounts Strap and Roller-Chain Mounts Push-Pull Mounts Comparison of Dynamic Relaxation and Finite-Element Analysis Techniques References MOUNTING LARGE VERTICAL-AXIS MIRRORS Introduction Ring Mounts Air Bag (Bladder) Mounts Multiple-Point Supports Metrology Mounts References MOUNTING LARGE, VARIABLE-ORIENTATION MIRRORS Introduction Mechanical Flotation Mounts Hydraulic/Pneumatic Mounts Center-Mounted Mirrors Mounts for Double-Arch Mirrors Bipod Mirror Mounts Thin Face Sheet Mirror Mounts Mounts for Large Space-Borne Mirrors References DESIGN AND MOUNTING OF METALLIC MIRRORS Introduction General Considerations of Metal Mirrors Aluminum Mirrors Beryllium Mirrors Mirrors Made from Other Metals Mirrors with Foam and Metal Matrix Cores Plating of Metal Mirrors Single-Point Diamond Turning of Metal Mirrors Conventional Mountings for Metal Mirrors Integral Mountings for Metal Mirrors Flexure Mountings for Larger Metal Mirrors Interfacing Multiple SPDT Components to Facilitate Assembly and Alignment References OPTICAL INSTRUMENT STRUCTURAL DESIGN Introduction Rigid Housing Configurations Modular Design Principles and Examples A Structural Design for High Shock Loading Athermalized Structural Designs Geometries for Telescope Tube Structures References ANALYSIS OF THE OPTO-MECHANICAL DESIGN Introduction Failure Predictions for Optics Stress Generation at Opto-Mechanical Interfaces Parametric Comparisons of Annular Interface Types Bending Effects Due to Offset Annular Contacts Effects of Temperature Changes Effects of Temperature Gradients Stresses in Cemented and Bonded Optics Due to Temperature Changes Some Effects of Temperature Changes on Elastomerically Mounted Lenses References APPENDIX A: UNITS AND THEIR CONVERSION APPENDIX B: SUMMARY OF METHODS FOR TESTING OPTICAL COMPONENTS AND OPTICAL INSTRUMENTS UNDER ADVERSE ENVIRONMENTAL CONDITIONS APPENDIX C: HARDNESS OF MATERIALS APPENDIX D: GLOSSARY INDEX

Distribution of light at and near the focus of high-numerical-aperture objectives

Abstract: Classical diffraction theory is used to investigate the effects of high numerical aperture on the focusing of coherent light. By expanding the diffracted beam in plane waves, we show that the lens action can be expressed as a succession of three Fourier transforms. Furthermore, polarization effects are included in the model in a natural way. Some numerical results of the theory are also presented.

Liquid crystal spectacles

Abstract: A liquid crystal spectacle includes a pair of liquid crystal lenses and a frame holding the lenses. The frame has a pair of temples and a pair of ear pieces attached individually to the temples. Each ear piece houses a battery for supplying the voltage to the corresponding lens. Each temple houses a regulator circuit for regulating the voltage supplied from the battery to the lens, thereby controlling the refractive index of the lens.

Two-dimensional scanning photo-electric microscope

Abstract: A scanning type optical microscope comprising a pair of light deflectors disposed between a laser light source and an objective lens for performing two-dimensional scanning of an object requiring observation by varying the incidence angle of a light entering the objective lens, and a pair of split detectors receiving a light coming from said object, wherein the light deflectors are disposed at the position of the pupil of the objective lens or at a position conjugate therewith or in their vicinity. This microscope has a high resolving power and allows an easy performance of a special microscopy and is convenient to handle. The paired detectors are arranged to be rotatable about an optical axis and allows free alteration of the orientation of differentiation of the differential observation image. A light-blocking plate can be provided within the detecting optical system for removing O-order diffraction light contained in the detection light, whereby permitting dark field microscopy at a very low cost.

Method for producing transparent plastic article

Abstract: A transparent plastic article with less internal strain is produced by successively polymerizing a monomer part by part with forming a gel state part between the already polymerized part and the unpolymerized part, or by polymerizing a monomer by means of a mold which can follow cure shrinkage of the monomer in order to decrease cure shrinkage. The article produced is particularly suitable for optical applications such as an optical disc, a lens and a prism.

Depth response of confocal optical microscopes.

Abstract: The on-axis intensity response of a confocal scanning optical microscope was measured for an objective of numerical aperture 0.9. The data compare favorably with theoretical calculations obtained by numerical integration of the standard theory, provided that lens aberrations are taken into account. The invariance of the shape of the central lobe to surface roughness and tilt is also demonstrated.

Compact zoom lens

Abstract: A compact zoom lens including, from front to rear, a first lens unit of positive power, a second lens unit of negative power, a third lens unit of positive power and, if desired, further a fourth lens unit, with the separations between the first and second units, between the second and third units and between the third and fourth units being made variable to vary the focal length of the entire system, wherein as the focal length is varied from the shortest to the longest value, the first and third units move axially forward, and the third unit is provided with a positive lens having an aspherical surface.

Two dimensional laser diode array

Abstract: A two dimensional laser diode array is disclosed for use in optical data storage consisting of rows and columns of individual lasers diodes, each one having a separate collimating lens. The array is imaged down onto an optical recording medium which is moving relative to the image of the array in order to generate scanning. The diodes in the array are staggered in the direction perpendicular to the scanning direction to achieve an apparent spacing lower than the actual spacing.

Ultraviolet radiation and blue light blocking polarizing lens

Abstract: A lens (10) that substantially blocks horizontally polarized light and selectively blocks wavelengths between 300 and 549 nanometers. The selective blocking is controlled by a sharp cut-on filter (14) selected to cut-on at either 450, 500, 515, 530, or 550 nanometers. The specific blocking and cut-on point selected is dependent upon the ultimate usage/environment of the lens (10). If a 450 cut-on filter is selected, wavelengths between 300 and 449 nanometers are blocked before a cut-on occurs at 450 nanometers; similarly, a 550 cut-on filter blocks wavelengths between 300 and 549 nanometers before a cut-on occurs at 550 nanometers. The lens (10) also allows 30 to 40 percent of wavelengths over 625 nanometers to be transmitted. The filter (14) in combination with the polarizer (16) blocks harmful Ultraviolet radiation and blue light. While a beneficial and calming effect is achieved by wearing only blue-blocking lenses, the addition of the polarizer (16) substantially enhances the calming effect and the improvement of vision without visual discomfort.

Clinical results of hydrogel lens implantation

Abstract: Polymethylmethacrylate has proven to be a useful intraocular lens (IOL) implant material and remains the most widely used material for the fabrication of IOLs. Complications, however, from IOL implantation still occur. A hydrogel lens has been designed for posterior chamber placement. A clinical study from August 1983 to June 1985 was undertaken to determine the safety and efficacy of this new lens manufactured from 38% poly HEMA. The noninhammatory postoperative complications were limited to lens decentration and opacification of the lens capsule. Three cases of posterior capsule opacification required YAG laser eapsulotomy. Laser- capsulotomy is feasible and the lens appeared to be more resistant to damage from the YAG laser than polymethylmethacrylate lenses. In general, the material appeared to be well tolerated and there have been no cases of persistent iritis or clinically detectable cystoid macular edema. If the visual acuity outcome by age decade for all patients irrespective of follow-up time is considered, 92% of patients achieved 20/40 or better corrected visual acuity.

Profile-measuring light probe using a change in reflection factor in the proximity of a critical angle of light

Abstract: A profile-measuring light probe includes: an illuminator for irradiating a fine spot of light on a subject to be measured; an objective lens for forming an image of the fine spot on an image plane; and a relay lens for converting the light from the fine spot into a generally parallel ray. Further, the light probe includes a window plate constituted by an entrance prism for taking in the generally parallel ray emitted from the relay lens; a flat glass for subjecting the taken-in ray to multiple internal reflections and transmitting the same, and an exit prism for outputting the ray thus transmitted to the outside. The light probe measures the distribution of light quantity of the light emitted from the window plate to thereby measure a profile of the subject to be measured. With the above-described arrangement, it becomes possible for the light probe to perform the measuring through the utilization of a change in reflection factor of a light inciding in the proximity of a critical angle without using a critical angle prism.

Instrument for measuring the topography of a surface

Abstract: An instrument for measuring the topography of a surface, comprising a light transmitting device for transmitting a light beam onto the surface; a light receiving device for receiving light reflected by the surface; a detector for detecting the position of the received light relative to the optical axis of the light receiving device; and means for providing relative movement between on one hand the light transmitting (10,L1,L2) and light receiving (L3,L4,8) devices, and on the other hand the surface (2) to be measured. According to the invention the optical axis (11) of the light transmitting device (10,L1,L2) is arranged to form a small angle (γ 1 ) with the normal to the median plane (13) of a workpiece surface (2) to be measured. The angle (γ 1 ) is smaller than about 15°. The optical axis (9) of the light receiving device (L3,L4) forms a right angle, or substantially a right angle (8) with the optical axis of the light transmitting device. The detector (8) is position-responsive, and an image magnifying lens (14) is located in front of the detector.

Intraocular lens with tapered haptics

Abstract: An intraocular lens for use as an artificial lens implant is disclosed. The intraocular lens includes an optical lens body having a periphery and two curved, elongated and resilient haptic members for positioning and supporting the lens in the eye. Each haptic member has an inner or root end and an outer or free end. The haptic member are integrally formed with the lens body as a one-piece construction at the root ends thereof. The haptic members extend outwardly from the lens body along an arc exterior to the periphery of the lens body. Each haptic member has at least a portion thereof tapered or reduced in cross sectional dimension in a direction therealong from the root end toward the free end.

Variable refractive power, expandable intraocular lenses

Abstract: Disclosed are intraocular lenses which have an expandable or fillable bag means comprising the central lenticular portion of the lens and lenses which are expandable by filling chambers within a flexible central lenticular portion. The central lenticular portion additionally can comprise a solid lens portion. The expandable bag means or chambers are filled correlating to a desired refractive power after placement in the eye. The intraocular lenses can be inserted in the eye through relatively small incisions (less than about 4 mm). Subsequent changes in refractive power can be accomplished without removing the implanted intraocular lens and with minimal or no trauma. The intraocular lenses can be implanted in either the posterior chamber or capsular bag.

Accommodating intraocular lens and lens series and method of lens selection

Abstract: This invention relates to an improved aspheric posterior chamber intraocular lens and lens series of said novel intraocular lens, which lens is used as a replacement within the eye for the absent human crystalline lens, and a simplified method of selecting a lens from said lens series for use in a given eye. The novel lens of this invention is designed to have a continuously and regularly increasing refractive power from its axis peripheralward in its optically active area and to achieve the following results: the correction of the axial refractive error of the aphakic eye in which it is placed, and the production of clear central vision over a continuous range of distances from far to near, where far is defined as six meters and beyond, and near or reading distance is defined as generally 40 cm from the eye but may be as close as 33 cm.

Excimer Laser-Based Lithography: A Deep Ultraviolet Wafer Stepper

Abstract: A deep UV projection system has been developed by modifying a commercial step and repeat exposure tool to operate at 248nm with an all-quartz lens and a KrF excimer laser. The lens is a 5X reduction lens with a minimum field size of 14.5 mm and a numerical aperture which is variable from 0.20 to 0.38. This produces a practical resolution of 0.5μm over the 14.5 mm field, with 0.4μm resolution achievable in a lab situation. Furthermore, by reducing the numerical aperture it is possible to print 0.8Am lines and spaces over a field larger than 14.5 mm with depth of focus greater than ±2μm. The data presented are results of extensive resolution studies as well as applications to real submicron devices. Some of the advantages and limitations of laser-based lithography are discussed, including possible directions for new laser development.

Optical coupling device

Abstract: An output light beam from a semiconductor laser is converged by a lens system or a fine optical fiber with a small core diameter The converged light beam is incident upon a part of the light receiving end face of a tapered optical fiber which is greater in area than the other end face thereof which is connected to one end of an optical fiber The reflected light beam in the multi-mode optical fiber because of discontinuous portion is substantially prevented from returning to the semiconductor laser, so that the adverse effects on the semiconductor laser by the reflected beam can be minimized

Refractively scanned interferometer

Abstract: A modified Michelson type of interferometer having a pair of substantially identical refractive prisms, each having a cross sectional shape of 1/2 of a hexagon, the division being along a line bisecting opposite sides of the hexagon, where each of the prisms has a side for beam input or output, a side that is coated to provide a mirror for beam reflection and a beamsplitter coating applied to one of the two surfaces along the line of division. Additionally, a collimating and/or focusing lens may be integral with the prism having the input or output side, such that linear, constant speed, relative scanning of the prisms in the direction of the line of division of the prisms enables the elimination of the mounting of all components, made a part of or attached to the prisms, to an optical bench.

Refracting solar energy concentrator and thin flexible fresnel lens

Abstract: A solar energy concentrator (20) including a thin flexible fresnel lens (24) for focusing incident solar radiation not normal to the lens (24) onto a target area (26) by refraction. The fresnel lens (24) is supported or suspended above the target area (26) by a frame (22) and folded along at least one line or region (28) parallel to the refractive prisms (32) of the lens (24) which are generally parallel to the axis of the target area (26) whereby the fresnel lens (24) opens toward the target area (26). Thus the fresnel lens (24) is so positioned so as to allow it to bow and flex under wind loads, gravity and other environmental factors without causing significant deterioration in the efficiency of the system.

Optical mixing/demixing device

Abstract: An optical mixing/demixing device is provided comprising a series of solid, light transmitting blocks, each having opposed, front and rear parallel, planar faces, coated with optical interference multilayer coatings, and first and second light transmitting faces arranged one on each side of the front planar face. The blocks are packed side by side with a precision, light expanding and collimating lens on the first light transmitting face and further, similar precision lenses on each of the second light transmitting faces. The first and second light transmitting faces may also be coated with optical interference multilayer coatings that are pass band filters.

Illumination optical system

Abstract: An illumination optical system comprises a multi-beam generator which includes a plurality of each of two kinds of lens elements different in optical characteristics and which is interposed between a source for generating a collimated light beam and a light condenser. The multi-beam generator generates a large number of secondary light sources from the collimated light beam. The illumination optical system is capable of supplying illuminating light rays having an extremely uniform illumination distribution.