A lens configuration called the limiting lens has been studied which describes the highest power, shortest focal length system for a given cylindrical volume. We consider here the classification and study of lenses which are constrained to fit into small packages in terms of how close the configurations come to the limiting lens.

Distortion can be corrected in an image by placing a fourth-order aspheric optical element near the image plane. Moving the aspheric surface longitudinally changes the amount of distortion added by the aspheric surface without changing the paraxial image. This ability to readily adjust the amount of image correction can be a powerful design tool for distortion-critical optical systems, such as digital optical computers. Third order astigmatism limits the performance of distortion correctors and may be eliminated by adding another fourth-order aspheric surface. Example elements were fabricated using diamond turning and were shown to introduce distortion without significantly degrading image quality. Three arrangements of distortion correctors are discussed: a single-element plano-aspheric arrangement, an anti- symmetric two-element arrangement, and a biaspheric arrangement in which distortion is not adjustable.

In any lens design problem, the first and most important step in the design process is the selection of the best design starting point, or design form, for the problem at hand. While many publications are available which address the selection of a design form for common optical problems, there is little available in the literature to assist the optical designer who is performing a conceptual design trade off in specialized areas of interest, such as UV microscopy. Given the advancement of short wavelength systems utilized in the semiconductor manufacturing industry, where the short wavelength is used in conjunction with high numerical apertures to provide increasingly smaller spot sizes, the once esoteric field of UV microscope objective design has moved to the forefront of the theater of optical design. This paper addresses the fundamental differences between the available UV objective starting points in the broadest possible terms within the context of varied system level constraints, and is intended to serve the designer as a vehicle for selecting the design form which will best suit the task at hand.

While distortion in a three mirror system is something we typically have to live with, certain methods available during the optimization process seem more amenable to controlling it than others. A variety of these distortion controlling techniques are discussed here, and numerical results are shown.

A new form of the Three Mirror Anastigmat (TMA) optical system is introduced having embedded features that greatly advance state-of-the-art of its manufacturability. A simple fabrication and alignment process is realized by forcing the primary and tertiary mirrors to share a common vertex and all mirrors to share a common axis. The primary-tertiary mirror pair is fabricated on a common substrate with single point diamond turning, eliminating the need for aligning these two elements. Design examples and fabrication data for reimaging and nonimaging telescopes will be presented illustrating benefits of the common vertex construction.

The ATLAS (Airborne Terrestrial Applications Sensor) system is a 15-channel imager for remote sensing applications currently under development at the NASA Stennis Space Center. This paper describes the optical design of the scan head optics, which include the linescan mirror, Dall-Kirkham telescope, collimator, and three spectrometers. The sensor package has a 7.5-inch entrance aperture with a 2.0 mrad ifov, total field of view of 73 degrees, and scan rates adjustable in the range 6 - 50 rev/sec. Spectral coverage is provided in the visible and near infrared (VIS/NIR, 0.45 - 0.90 micrometers , 6 channels) using three spectrometers. The three spectrometers have a modular design for future applications growth. Design and specifications for the telescope, special dichroics, gratings, imaging lenses and other components for the spectrometers, will be described. Detector arrays for the three spectrometers, and built-in sources for radiometric calibration, will also be discussed. Finally, results of overall ATLAS systems performance analysis on optical throughput, SNR, NETD, etc, will be presented.

The Floptical 3.5 inch floppy disk drive uses optical track sensing for 'Very High Density' (VHD) mode, and is also downward compatible with the DD and HD formats. A new optical head for Floptical Technology developed by Iomega uses a laser diode and a Computer Generated Hologram (CGH) to accomplish high signal levels and signal-to-noise ratio, long depth of focus, and low manufacturing cost. The new optical head uses a detection scheme of projecting--with very long depth of focus--a patch of sinusoidal grating pattern with the same spacing as the VHD tracks onto the disk surface, and detects the amount of reflected light. The track detection function is the convolution of the light pattern and the reflectivity function of the disk tracks. Depth of focus of the head is hundreds of microns. Integration across several tracks improves signal-to-noise ratio of the tracking signals. Utilization of a laser diode provides high signal levels. A computer generated binary hologram replaces several conventional optical elements. The HOE is replicated at much lower cost than conventional optics, and mechanically it simplifies head assembly, saving head cost on both counts.

Much has been written in the past four to five years on the application of hybrid refractive/diffractive elements in infrared optical design. We are now beginning to see several excellent examples of actual systems which utilize such components. Little has been written, however, on the use of hybrid elements in lens systems for staring focal plane arrays which require 100% cold stop efficiency (CSE). Most designs presented in the literature have been for uncooled staring arrays. The purpose of this paper is to examine the requirements that present MWIR focal plane arrays (FPAs) place on the objective, and to investigate the role hybrid diffractive optical elements (DOEs) play in the solution of this imaging problem. We briefly examine the requirements imposed by the next generation MWIR FPAs to show that hybrids can play a role in compact, lightweight systems of the future. In addition, we illustrate areas of future design activity such as passively athermal IR objectives and wide angle IR lenses.

This paper will review fundamental aspects of an innovative approach to multi-spectral imaging by exploiting variable electronic conductance properties of semi-conductor and semi- metal materials to create a tunable, bandpass infrared filter. The filter would operate through use of a controlled wavelength dependent change in optical reflectance that is a characteristics of electrochromic and photochromic materials. The reflectance effect is predicted by modified Drude free electron models for metallic-like conducting systems. As a design example, a filter based on doped tungsten trioxide (WO₃), will be presented. Another filter design resulting in an all solid state device would use properly constructed and doped silicon or GaAs and operate at cryogenic temperatures. These filter designs use a Michelson interferometer configuration with different reflective structures in the two 'arms'. Wavelength control is provided through electric field induced changes to the electronic charge carrier concentrations found in a thin layer at the surface of the active mirror materials.

The focal plane of an infrared seeker was plagued with ghost images and nonuniform stray light irradiance. Teledyne Brown Engineering was tasked to determine the irradiance source and propose inexpensive solutions to the problems. First order analysis approximately modeled the focal plane irradiance and showed a serious flaw in the design. A design flaw allowed normal internally emitted thermal radiation to develop into a high level, nonuniform, focal plane irradiance. Exact ray tracing software, developed by the author, computed focal plane irradiance distributions which closely matched measured distributions. The software performs a non-sequential surface ray trace, splitting rays at partially reflecting surfaces (using a recursive algorithm), and computes internal thermal emission. The stray light problems could have been avoided in a design with the cold stop as the system aperture stop. This paper shows the method of analysis, results, and proposed solutions to the problem. This work demonstrates how infrared optical design requires precautions and considerations. Methods and tools which work well in visible optical design may not work in infrared optical design.

The determination of the radiant power distribution at the focal plane is necessary for the numerical prediction of sensor radiometric performance. In a diffraction limited system with a circular pupil and central obscuration, the energy distribution can be calculated by numerical integration of the appropriate Bessel function(s). However, not all optical systems are that simple. The determination of the energy distribution for non-diffraction limited systems and systems having arbitrary pupil shapes is of practical importance but requires a more complicated analysis. The paper provides, in a 'cookbook' fashion, the algorithms necessary for the prediction of the focal plane power distribution in diffraction and non-diffraction limited optical systems with arbitrarily shaped pupils. The sensor pupil function, comprised of amplitude and phase, may be defined by the optical design or may be obtained by interferometric measurements performed on an existing system. The pupil function, expressed in complex notation, is processed through a two-dimensional fast Fourier transform, interpolated and scaled to provide the focal plane energy distribution. In addition to an algebraic description of the necessary algorithms, the paper includes code written in the C- language and numerical examples suitable for validation.

We describe the optical, mechanical and servo designs for a motorized, two-FOV (field of view) IR objective lens for use in the 8 - 12 micrometers spectral band. The FOV is changed by moving lenses axially instead of the more traditional approach which is to add and remove lenses. The advantages of this approach include: simple mechanics, since a single mechanism can be used for both adjusting focus and changing FOV; only one lens group need be moved; no stow space is needed for removed lenses; and fewer total lenses are needed (four elements). The lens is used with a low-cost, uncooled focal plane array. This dictates relatively fast F- number, large image format (F/1.1, 7.8 degree(s) narrow FOV, 155-mm narrow-field focal length), and low cost. This combination of wide field and large collecting aperture pose a difficult optical design challenge. The lens meets a range of military environmental requirements including immersion in one meter of water. We describe how the requirements were met. We have fabricated and tested five lenses and we describe the assembly and testing process and present a summary of test results.

The U.S. Navy has several hundred P3 Orion Aircraft which utilize the AN/AAS-36 Texas Instruments FLIRs. The system is an 8 - 12 micrometers long wave IR imaging system using a linear HgCdTe detector array. The FLIR optics consists of the classic common module imager which is a 3-element IR lens with an external scan mirror which produces the linear pushbroom scan over the linear detector array. This system is actually a dual field of view, and a 3-element Galilean afocal telescope located in front of the imager is used for a 3X magnification. In the wide field of view mode the imager is simply used alone looking out into object space, with the 3X afocal telescope rotated with its optical axis orthogonal to the imager axis. In order to switch to the narrow field of view, the afocal telescope is rotated 90 degree(s) and the user acquires a net 3X magnification to the imagery. The loss of imagery during the field switching operation has always been seen as a problem, and it would be far more desirable to have a continuously varying magnification instead. For this reason, the Navy put out a Small Business Innovation Research solicitation in 1989 with the intent of developing a continuously varying IR zoom lens to retrofit into onto the TI FLIR. OPTICS 1, Inc. completed Phase I of this SBIR which demonstrated feasibility of the design concept, and we have been under contract on the Phase II program since April, 1990.

In order to realize a compact and light-weight zoom lens for video camera, we have applied the aspherical plastic lens technology. In this design, we found the methods, elimination of the lens group, and replacement from a glass lens to a aspherical plastic lens.

This paper describes integrated intelligent system MEX—! for optical zoom lens design. It consists of several sub—expert systems which coordinate work with each other. Every sub—expert system has i ts knowledge base. HEX—i applys hi erarchi cal and di stri buted control strategy. The meta system is used to coordinate the work of the sub—expert systems. Blackboard (BB) system is used as communication medium. MEX—1 system structure can also be abstracted as a general shell of an integrated intelligent system to solve complex domain problems. We also gi ye an exampi e for opti cal zoom lens desi gn.

Many problems of rundamental and. applied. physics lie in the field. of researches connected with IR—rad.iations propagation and. interaction in matter. It is common in these researches to deal with use or multilayer interrerence dielectric structures ror solution of some problems of clarifying, riltering, splitting etc. Related long wave character or IR range and existance in it of a limited number or dielectric materials with low absorption, however, lead to some dirriculties, sometimes unavoidable, ror successrul solution or problems or design or IR optics systems. In this report optical and. spectral properties or a new class or layer—nonunirorm media (so—called superrine stratified structures (555)) are presented. They allow to avoid some problems in creating IR optics systems.

The Mars Observer Camera (MOC) is one of the instruments aboard the Mars Observer Spacecraft to be launched not later than September 1992, whose mission is to geologically and climatologically map the Martian surface and atmosphere over a period of one Martian year. This paper discusses the events in the development of MOC that took place in the past two years, with special attention given to the implementation of thermal blankets, shields, and thermal control paints to limit solar absorption while controlling stray light; vibration testing of Flight Unit No.1; and thermal expansion testing. Results are presented of thermal-vac testing Flight Unit No. 1. It was found that, although the temperature profiles were as predicted, the thermally-induced focus displacements were not.

The Ultraviolet Coronagraph Spectrometer is a state of the art instrument which will be flown aboard the ESA SOHO spacecraft in 1995. A major objective of the SOHO is to investigate the solar corona and the solar wind by measuring parameters of the plasma, both in the source and acceleration regions, and in interplanetary space. The UVCS will provide ultraviolet spectroscopic diagnostics of temperature, density, and outflow velocity for coronal ions located between the base of the solar corona and 10 solar radii. The requirements placed on the UVCS telescope structure by the science and the spacecraft are challenging. Obtaining this scientific data requires that the telescope maintain pointing stability within a few arc-seconds in a transient thermal environment and an imaging stability within a few microns. Strict mass allowances permit only 22 kg for the 2.5 meter long telescope structure out of a total instrument allotment of 124 kg. The instrument is required to have a high minimum natural frequency of 70 Hertz and withstand launch inertia loads in excess of 18-G's while kinematically supported.

The Ultraviolet Coronagraph Spectrograph (UVCS) is an optical instrument to be flown on the European spacecraft Solar Heliospheric Observatory (SOHO) to the sun-earth L1 point. The stability requirements of the instrument require the moisture content of the pseudoisotropic composite material not to exceed 0.06% during alignment and calibration. This paper describes the steps necessary to meet this requirement. These steps include a dynamic moisture content analysis, selection of bake out conditions and moisture controls, verification sampling, and use of witness specimens to monitor the moisture content during the prelaunch life of the structure.

Advanced composite materials are well suited for stable space structures due to their low Coefficient of Thermal Expansion (CTE), high stiffness and light weight. For a given design application, composite hardware can be tailored for strength, stiffness, CTE, and Coefficient of Moisture Expansion (CME). Computer modeling and laminate testing of high modulus graphite/epoxy tubes were evaluated for compressive strength, stiffness, CTE, CME and microcracking. Thermal cycling and microcracking effects on CTE were evaluated. Thin graphite/epoxy plies exhibited reduced microcracking. A zero CTE thin wall tube design resulted from the development program. Recent work on low moisture absorption resin systems is also discussed.

The first production lot of 50 units of metal matrix composite mirrors for the Leopard I tank fire control system was recently completed by Optical Corporation of America (OCA), Garden Grove, California. The mirror substrates were finish machined from forgings of Optical Grade SXA^TM metal matrix composite manufactured by Advanced Composite Materials Corporation (ACMC), Greer, South Carolina. Use of forgings rather than hot pressed billet yields more efficient use of material and reduces machining time, resulting in lower cost. The mirrors were fabricated by a process sequence of machining, thermal stabilization, electroless nickel plating, polishing, and coating with a high efficiency, laser damage-resistant optical coating. The mirrors are used in the fire control system for a day channel (direct view) and near infrared (CCD), a muzzle reference system laser transceiver, a laser range finder, and an infrared thermal imaging system. SXA composite was chosen over competitive mirror materials (glass and beryllium) because of its high specific strength and stiffness, good stability, and moderate machining cost. The mirrors exhibit excellent stability and optical performance. Field trials of prototype mirrors in fire control systems have proven successful.

Calculations are presented of the coefficient of thermal expansion (CTE) of the radius of curvature of the reflector face sheets made of a quasi-isotropic composite. It is shown that, upon cooling, the change of the CTE of the focal distance of the mirror is equal to that of the radius of the curvature of the reflector face sheet. The CTE of the radius of the curvature of a quasi-isotropic composite face sheet depends on both the in-plane and the out-of-plane CTEs. The zero in-plane CTE of a face sheet does not guarantee mirrors with no focal length changes.

One of the critical technology needs of large precision reflectors for future astrophysical and optical communications satellites lies in the area of structural materials. Results from a materials research and development program at NASA Langley Research Center to provide materials for these reflector applications are discussed. Advanced materials that meet the reflector panel requirements are identified and thermal, mechanical and durability properties of candidate materials after exposure to simulated space environments are compared. Results from analytical studies to define material properties that control laminate properties and reflector deformation are discussed. A parabolic, graphite-phenolic honeycomb composite panel having a surface accuracy of 70.8 microinches RMS and an areal weight of 1.17 lbm/ft² was fabricated with T50/ERL1962 facesheets, a PAEI thermoplastic surface film, and Al and SiO_x coatings.

Results are presented of a thermal design optimization study of the segmented GFRP primary reflector of the earth-orbiting Submillimeter Imager and Line Survey telescope. The paper examines the thermal requirements of the primary reflector and the thermal environment of the telescope and describes the thermal design of the primary reflector. Particular attention is given to the geometric math model and the thermal math model of the telescope. A summary for the steady-state thermal performance of the optimized design is presented, showing that the optimized design has reduced, by an order of magnitude, structural spatial temperature gradients, which were earlier shown to be the most significant obstacle in maintaining the required telescope figure accuracy.

The stringent stability requirements of the Corrective Optics Space Telescope Axial Replacement (COSTAR) necessitates a Deployable Optical Bench (DOB) with both a low CTE and high resonant frequency. The DOB design consists of a monocoque thin shell structure which marries metallic machined parts with graphite epoxy formed structure. Structural analysis of the DOB has been integrated into the laminate design and optimization process. Also, the structural analytical results are compared with vibration and thermal test data to assess the reliability of the analysis.

Cost and weight savings achieved by the use of composites have allowed these materials to displace their metal counterparts in space applications. Epoxy matrix based carbon fiber reinforced composites, such as Fiberite 934, have been used for a number of years. Relative to these systems, cyanate esters offer a number of unique attributes such as excellent hydrophobicity and electrical properties, reduced residual stress and better microcrack resistance, and improved radiation resistance. The significant reduction in water sorption and the low response to uptake make it possible to achieve much improved dimensional stability and reduced outgassing. These features may be used to advantage in electro-optical applications in space. ICI Fiberite has developed cyanate ester based prepreg systems that are penetrating the satellite, military radome and structural aerospace markets. Features of these systems will be presented and the properties of the cyanate ester based prepreg, Fiberite 954- 3, will be compared to those of Fiberite 934.

Structural epoxy resins used in the fabrication of composite structures for spacecraft applications absorb significant amounts of water. This moisture absorption results in swelling of the structures during fabrication and assembly and subsequent desorption shrinkage in space. Reduction of this effect will be required for development of dimensionally stable large advanced space structures. In the last several years modified epoxy resins, cyanate esters and cyanate esters/epoxy resins have been developed with lower moisture absorption structures to address this issue. Work has continued for several years on the evaluation of high modulus Pitch 75 laminates made using modified low moisture absorption epoxy and cyanate systems to developed structural and thermophysical data for use in the design of stable structures. This paper describes the evaluation of moisture absorption and mechanical properties of unidirectional and quasi-isotropic Pitch 75 laminates made from selected cyanate esters and cyanate ester-epoxy resins.

Dimensional stability in composite structures has mainly focused on near-zero CTE, high- modulus fiber/epoxy resin systems. However, hygrothermal stability has been demonstrated to be a serious concern for structures moisturized on earth and dried in orbit. Composite sealing techniques have been developed to prevent this moisture absorption and desorption with the concomitant dimensional changes. New resin system are being developed which absorb significantly less moisture and show promise as optional systems in dimensionally stable structures. These resin systems have not been evaluated for their physical and mechanical properties. This paper describes the testing of various high-modulus, cyanate ester resin systems for evaluation in dimensionally stable composite applications. Physical testing included moisture absorption testing, coefficient of thermal expansion, and hygrothermal strain change. Mechanical testing included tensile, compression, Iosipescu shear, and bonded joint allowables. A comparison of the thermomechanical properties for the cyanate ester resin systems is made with a P75S/ERL1962 baseline epoxy resin systems.

Theoretically, the use of composite structural materials with a low coefficient of thermal expansion (CTE) and a careful choice of a laminate should yield a structure which is nearly insensitive to thermal loading. However in reality experience has shown that tolerances associated with parameters such as layup angles, layer thicknesses, and basic properties such as Young's modulus and fiber CTE can combine to yield a variation in CTE that can be as large, or larger, than the predicted nominal value. It is difficult and very expensive to measure and verify the CTE of structures which nominally possess a CTE in the range of +/- 0.1 x 10 exp -6 in/in/F. This paper presents a statistical approach which is based on the measured variation of physical properties of the materials used and discusses a method for making an assessment of the statistical CTE property variation. Using these statistics, a finite element based Monte Carlo methodology is discussed. A composite parabolic reflector numeric example is provided.

This paper describes the application of the finite element method to calculate the dynamic response of a spinning polygon, motor, and motor housing used in xerographic printers. Initially, different levels of model sophistication were evaluated showing convergence to a representative model. Using the converged model, the dynamic response of the polygon mirror was evaluated from the effects of base excitation. Frequency correlation in the 0 to 1000 hertz range was demonstrated to be better than 10% when compared to a dynamic modal test. Mechanical gain correlation at the fundamental rotor resonance was of the same order as the modal test with amplitude variations attributed to the assumed damping of the model, and differences between empirical and analytical response locations. Conclusions and recommendations on future work are also cited.

The advances made in lightweight mirror technology over the past several years has been dramatic. Progress has been made in manufacturing precision, lightweighting, size, mirror segmentation, thermal stability, and asphericity. Minimization of mirror weight can be highly influenced by these factors. When considering active mirror technology, it is necessary to include the actuators as part of the effective mirror weight, since they are integral parts of the mirror system and influence figure accuracy, dynamic characteristics, and other issues associated with mirror performance. A comparison of active facesheet designs (solid versus lightweight) is presented, which illustrates the approach to minimizing mirror weight by optimizing the number of actuators.

The design of the mount for the outer pair of Advanced X-ray Astrophysics Facility (AXAF) optics for the Verification Engineering Test Article-I (VETA-I) hardware for initial performance test was a challenging task. Extensive analysis of mirror strains induced by the mounting hardware during assembly was required to ensure that the imaging tests at Marshall Space Flight Center would be successful. This paper describes the techniques used to design the mirror cell to insure that the X-ray tests would accurately represent the quality of the mirror surfaces and minimize errors due to the effects of mounting and gravity. The measures taken to compensate for the large gravity effects during testing are discussed in detail.

A modified Serrurier truss was designed to support a beam collapser for the USNO Optical Interferometer. The truss was designed to maintain the primary and secondary mirrors within the allowed specified optical and stress tolerances under gravity, wind, thermal, and earthquake loading. A NASTRAN finite element model and closed-form equations were developed to design the truss members.

The merits of a tangential spider vane support as opposed to a traditional radial vane support for telescope secondary mirrors are examined. Considerable interest in tangential spider design has been shown in recent large telescope projects. This configuration is used to limit vibration during the operation of the chopping secondary by improving the torsional stiffness.

The Soft X-ray Telescope (SXT) is one of four major instruments that constitute the payload of the NASA-Japanese mission YOHKOH (formerly known as Solar-A), scheduled to be launched in August, 1991. This paper describes the design of the SXT, the key system requirements, and the SXT optical and structural systems. Particular attention is given to the design considerations for stiffness and dimensional stability, temperature compensation, and moisture sensitivyty control. Consideration is also given to the X-ray mirror, the aspect telescope, the entrance filters, the mechanical structure design, the aft support plate and mount, the SXT finite element model, and other subsystems.

The paper discusses the effect of thermal gradients on the optical performance of the primary mirror of Mars Observer Camera (MOC), which will be launched on the Mars Observer spacecraft in September 1992. It was found that mild temperature gradients can have a large effect on the mirror surface figure, even for relatively low coefficient-of-thermal-expansion materials. However, in the case of the MOC primary mirror, it was found that the radius of curvature (ROC) of the reflective surface of the mirror changed in a nearly linear fashion with the radial temperature gradient, with little additional aberration. A solid-state ROC controller using the thermal gradient effect was implemented and verified.

A lens mount has been designed to accommodate both thermal excursions and severe dynamic loadings without introducing significant aberrations into the optic or incurring permanent alignment shifts. The mount was analyzed and tested over a wide range of environmental conditions and found to meet all of its performance goals. This paper illustrates, in detail, the methodology employed in the design of this mount assembly including manufacturability and performance analysis and testing.

A procedure is described wherein a common method for locating good starting points to the Cooke design is adapted to the problem of the reflective triplet. The procedure begins with a determination of some physical and first-order criteria. This criteria is employed to produce a binary function which expresses the acceptable areas of solution space. Candidate systems in their all-spherical element form are then considered for their relative departure from aplanatisism. A three-dimensional topography is produced from the physical criteria's binary data and the design's third-order error content. Selected points on the topography are investigated for their relative levels of aberration. The added freedom of general conic deformity is then permitted to determine the design's potential as an aplanatic, flat-field anastigmat.