Proceedings Volume 7793

Optical System Alignment, Tolerancing, and Verification IV

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Proceedings Volume 7793

Optical System Alignment, Tolerancing, and Verification IV

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Volume Details

Date Published: 20 August 2010
Contents: 6 Sessions, 19 Papers, 0 Presentations
Conference: SPIE Optical Engineering + Applications 2010
Volume Number: 7793

Table of Contents

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Table of Contents

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  • Front Matter: Volume 7793
  • Tolerancing and Optomechanics
  • James Webb Space Telescope Alignment and Metrology
  • Alignment and Optical System Analysis
  • Verification, Inspection, and Metrology
  • Poster Session
Front Matter: Volume 7793
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Front Matter: Volume 7793
This pdf file contains the front matter associated with SPIE Proceedings Volume 7793, including Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.
Tolerancing and Optomechanics
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Performance and tolerance sensitivity optimization of highly aspheric miniature camera lenses
Miniature camera lenses are currently manufactured at volumes over 1 billion units per year. In this high volume industry, design methods that improve tolerance to manufacturing errors result in improved yield and significantly reduced cost. Few, if any, design for manufacture methods have been developed for this solution space, which is vastly different than traditional design as it is dominated by highly aspheric optics and compact design forms. In this paper, five design for manufacture methods that were developed for traditional designs are examined for their efficacy in improving the as-built performance of a well-corrected injection molded miniature camera lens. Building on the results of the evaluation, a new design for manufacture method is developed which is highly correlated to the sensitivities associated with this solution space and requires little computational overhead. The new method generates 1.3 times the number of improved solutions and produces a design with 1.7X looser tolerances than the starting point.
Development of a photographic package printer: a case study
A specialty area in the commercial photographic industry involves simultaneously producing a plurality of high-quality photographs of varying size and shape from a single photographic negative or digital image. The images are formed on a large piece of photographic paper by a set of lenses having specific magnifications and appropriately located between the negative and paper. Package printers are typically reconfigurable to allow different sets of images to be created; however, such reconfiguration is time consuming. Most often, a package printer is configured and then devoted to a specific format. The case study presented in this paper covers the system requirements, design and fabrication of the various lenses, exposure and color balancing of the lenses, alignment and tolerancing. An interesting aspect of this package printer project was that the client literally built everything in-house including the mechanical housing, film and paper transports, lamp houses, lenses, and coatings. A critical element of the design, fabrication, and assembly of these package printers was tolerancing. Since a large number of these package printers was to be manufactured for their in-house, management needed assurance that the unit could be reasonably manufactured and would be reliable in the several plants around the world. The emphasis of this case study is on the challenge of producibility which required close attention to the capabilities of the various fabrication groups, assemblers, and technicians employed by the client. The project was successful and untold billions of photographs have been made by these package printers.
Conjugate selection for precision lens centering
The concept of centering a precision, symmetric lens system using a high-quality rotary table and an auto-focusing test instrument are well known. Less well known are methods of finding convenient, or easily accessible, lens conjugates on which to focus while performing the centering operation. We introduce methods of finding suitable conjugates and centering configurations that lend themselves to practical centering solutions.
James Webb Space Telescope Alignment and Metrology
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Relating axial motion of optical elements to focal shift
Katie Schwertz, J. H. Burge
In this paper, simple relationships are presented to determine the amount of focal shift that will result from the axial motion of a single element or group of elements in a system. These equations can simplify first-order optomechanical analysis of a system. Examples of how these equations are applied are shown for lenses, mirrors, and groups of optical elements. Limitations of these relationships are discussed and the accuracy is shown in relation to modeled systems.
Cryogenic testing of detector alignment of the Fine Guidance Sensor for the James Webb Space Telescope
Sandra Delamer, Sandy Beaton, David Aldridge, et al.
The development of the James Webb Space Telescope (JWST) is an international collaboration led by NASA in partnership with the European Space Agency and the Canadian Space Agency (CSA). The Canadian contribution to the mission is the Fine Guidance Sensor (FGS). The FGS-Guider images two fields of view onto two detectors. For testing, Optical Ground Support Equipment telescopes are used to simulate the image from the Observatory's Optical Telescope Element. The FGS Engineering Test Unit (ETU) comprises 2 functioning Guider channels: one fully functional channel with a Teledyne H2RG HgCdTe 5 micron cutoff detector, and another with an H2RG multiplexer in place of a detector. This paper reports on the results of cryogenic vacuum testing of the alignment of the final ETU instrument configuration. Images at ambient (from the H2RG multiplexer) and at cryo (from detector and H2RG multiplexer) were analysed to determine best focus and FGS field of view at cryogenic temperatures. The ETU test results for best focus, tip/tilt of focal planes, field of view location and size are well matched to the budgets and predictions and meet requirements for the FGS-Guider.
Primary mirror segment assembly integration and alignment for the James Webb Space Telescope
Conrad Wells, Mark Mallette, David Fischer, et al.
The Optical Telescope Element (OTE) consists of a 6.6 m, all-reflective, three-mirror anastigmat. The 18-segment primary mirror (PM) presents unique and challenging assembly, integration and alignment verification requirements. Each mirror segment is mechanically integrated with the Primary Mirror Backplane Support Structure (PMBSS) using compound angle shims to compensate for global alignment and local co-planarity errors. The processes used to determine the mechanical shim prescription, primary mirror alignment and integration, and placement verification are discussed. In an effort to reduce process uncertainty and program risk, the JWST program recently conducted a PMSA Integration Demonstration at ITT. Through this activity, full scale demonstrations of the Ground Support Equipment (GSE) and critical integration processes were successfully completed. The results of these demonstrations indicate that the equipment, processes, and procedures developed by ITT meet the critical requirements for PMSA placement.
Cryogenic performance of a high precision photogrammetry system for verification of the James Webb Space Telescope Integrated Science Instrument Module and associated ground support equipment structural alignment requirements
Maria D. Nowak, Paul E. Cleveland, Emmanuel Cofie, et al.
The James Webb Space Telescope (JWST) is a general astrophysics mission which consists of a 6.6m diameter, segmented, deployable telescope for cryogenic IR space astronomy (~35K). The JWST Observatory architecture includes the Optical Telescope Element and the Integrated Science Instrument Module (ISIM) element that contains four science instruments (SI) including a Guider. The alignment philosophy of ISIM is such that the cryogenic changes in the alignment of the SI interfaces are captured in the ISIM alignment error budget. The SIs are aligned to the structure's coordinate system under ambient, clean room conditions using laser tracker and theodolite metrology. The ISIM structure is thermally cycled and temperature-induced structural changes are concurrently measured with a photogrammetry metrology system to ensure they are within requirements. We compare the ISIM photogrammetry system performance to the ISIM metrology requirements and describe the cryogenic data acquired to verify photogrammetry system level requirements, including measurement uncertainty. The ISIM photogrammetry system is the baseline concept for future tests involving the Optical Telescope Element (OTE) and Observatory level testing at Johnson Space Flight Center.
Cryogenic metrology for the James Webb Space Telescope Integrated Science Instrument Module alignment target fixtures using laser radar through a chamber window
T. Hadjimichael, D. Kubalak, A. Slotwinski, et al.
The James Webb Space Telescope Integrated Science Instrument Module utilizes two fixtures to align the Optical Telescope Element Simulator (OSIM) to the coordinate systems established on the ISIM and the ISIM Test Platform (ITP). These fixtures contain targets which are visible to the OSIM Alignment Diagnostics Module (ADM). Requirements on these fixtures must be met under ambient and cryogenic conditions. This paper discusses the cryogenic metrology involving Laser Radar measurements through a chamber window that will be used to link photogrammetry target measurements used during ISIM structure cryogenic verification and the ADM targets, including evaluation of distortion introduced from the window.
Alignment and Optical System Analysis
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Characterization of an alignment procedure using an air bearing and off-the-shelf optics
L. Coyle, M. Dubin, J. H. Burge
We characterize the precision of five approaches used to align a series of targets over a distance of two meters. For many applications, an alignment telescope provides the necessary precision for positioning targets. However, for systems with tight tolerances, we must have a measure of the uncertainties in the alignment telescope to determine if it can truly meet the system requirements. We develop a procedure to measure the precision of each alignment approach and compare their performances. We use a telescope constructed from off-the-shelf optics and mechanics to determine if we can obtain alignment precision comparable to an alignment telescope of superior optical quality.
Design, assembly, and testing of the neutron imaging lens for the National Ignition Facility
Robert M. Malone, Brian C. Cox, Valerie E. Fatherley, et al.
The National Ignition Facility will begin testing DT fuel capsules yielding greater than 1013 neutrons during 2010. Neutron imaging is an important diagnostic for understanding capsule behavior. Neutrons are imaged at a scintillator after passing through a pinhole. The pixelated, 160-mm square scintillator is made up of 1/4 mm diameter rods 50 mm long. Shielding and distance (28 m) are used to preserve the recording diagnostic hardware. Neutron imaging is light starved. We designed a large nine-element collecting lens to relay as much scintillator light as reasonable onto a 75 mm gated microchannel plate (MCP) intensifier. The image from the intensifier's phosphor passes through a fiber taper onto a CCD camera for digital storage. Alignment of the pinhole and tilting of the scintillator is performed before the relay lens and MCP can be aligned. Careful tilting of the scintillator is done so that each neutron only passes through one rod (no crosstalk allowed). The 3.2 ns decay time scintillator emits light in the deep blue, requiring special glass materials. The glass within the lens housing weighs 26 lbs, with the largest element being 7.7 inches in diameter. The distance between the scintillator and the MCP is only 27 inches. The scintillator emits light with 0.56 NA and the lens collects light at 0.15 NA. Thus, the MCP collects only 7% of the available light. Baffling the stray light is a major concern in the design of the optics. Glass cost considerations, tolerancing, and alignment of this lens system will be discussed.
Active reconstruction and alignment strategies for the Advanced Technology Solar Telescope
The Advanced Technology Solar Telescope (ATST) is a 4m off-axis telescope with a Gregorian front end. At the time of its construction it will be the world's largest solar astronomical telescope. During scientific operations the ATST mirrors and structure will be deformed due to thermal and gravitational loading. The ATST team has developed a quasi-static alignment scheme that utilizes the wavefront sensing signals from at least one and as many as three wavefront sensors in the telescope science field of view, and active figure control of the primary mirror and rigid body control of the secondary mirror to achieve least-squares optical control of the telescope. This paper presents the quasi-static alignment model for the ATST, and three different active alignment schemes that are the damped least-squares control, force optimized control that defines a least-squares aligned state of the telescope subject to minimum primary actuator force, and pivot-point control of the secondary mirror. All three strategies achieve the desired minimum RMS wavefront error, but demonstrate different optimized states of the telescope.
Integration of differential wavefront sampling with merit function regression for efficient alignment of three-mirror anastigmat optical system
We first studied the characteristics of alignment performances of two computer-aided alignment algorithms i.e. merit function regression (MFR) and differential wavefront sampling (DWS). The initial study shows i) that, utilizing damped least square algorithm, MFR offers accurate alignment estimation to the optical systems with non-linear wavefront sensitivity to changes in alignment parameters, but at the expense of neglecting the coupling effects among multiple optical components, and ii) that DWS can estimate the alignment state while taking the inter-element coupling effects into consideration, but at the expense of increased sensitivity to measurement error associated with experiment apparatus. Following the aforementioned study, we report a new improved alignment computation technique benefitted from modified MFR computation incorporating the concept of standard DWS method. The optical system used in this study is a three-mirror anastignmat (TMA) based optical design for the next generation geostationary ocean color instrument (GOCI-II). Using an aspheric primary mirror of 210 mm in diameter, the F/7.3 TMA design offers good imaging performance such as 80% in 4 um in GEE, MTF of 0.65 at 65.02 in Nyquist frequency. The optical system is designed to be packaged into a compact dimension of 0.25m × 0.55m × 1.050m. The trial simulation runs demonstrate that this integrated alignment method show much better alignment estimation accuracies than those of standard MFR and DWS methods, especially when in presence of measurement errors. The underlying concept, computational details and trial simulation results are presented together with implications to potential applications.
Verification, Inspection, and Metrology
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Stiffening an off-axis beam compressor mount for improved performance
The Navy Prototype Optical Interferometer (NPOI) near Flagstaff, Arizona, makes use of separate smaller optical elements spaced along a Y-array and used simultaneously to simulate an equivalent single large telescope. The instrument is useful in generating and upgrading existing astronomical catalogues and investigating synthetic aperture optical imaging techniques. The NPOI is a joint collaboration between the US Naval Observatory and Naval Research Laboratory in collaboration with the Lowell Observatory. Stellar radiation (visible light) reflects off 35 cm diameter flat mirrors, also known as siderostats, toward a tilt-tip mirror, which reflects a 12 cm diameter beam through a multi-reflection relay transport system. To maximize the reflective area of the siderostat optics and achieve an increase by a factor of 8.5 in light collecting area, a beam compressor is to be installed between the siderostat and fast tip/tilt mirror. However, the present configuration of a prototype beam compressor mount (BCM) vibrates at unacceptable amplitudes, which makes it nearly impossible to optically align the mirrors. This paper presents the results of finite element analyses conducted to quantify the design limitations of the prototype beam compressor mount. The analyses indicated that the current configuration is too soft, with very low fundamental frequencies, which verified the difficulties encountered during alignment tests. Based on these results, design modifications have been proposed to increase the overall structural stiffness of the mount and increase its fundamental frequency of vibration. These modifications will mechanically stabilize the structure for the alignment of the optics, and allow integration of the compressor into the interferometer. The interferometer will then have the capability to capture more light from each siderostat and allow observations of fainter stellar targets. More generally, the results can be useful as a guide for engineers and scientists involved in the design of similar optomechanical structures.
Passive ranging metrology with range sensitivity exceeding one part in 10,000
Measurement of the distance to an object can be done in a number of ways based on system constraints such as minimum or maximum range, range accuracy, measurement update rate, and system power, with a considerable variation in resulting system complexity. Active approaches used in laser rangefinders yield submillimeter accuracy in laboratory or survey exercises while time-of- flight or flash LIDAR yields centimeter-scale range accuracy from mapping platforms in low Earth orbit. High ranging sensitivity, in excess of one part in 106, can be achieved, but generally requires fairly sophisticated control of the output pulse phase, shape, and energy, and also relies on fairly high speed pulse detection and processing. Passive approaches based purely on parallax imaging can determine distances to centimeter accuracies over moderate distances. The accuracy that can be achieved with this type of system is highly dependent on the overall SNR and the parallax angle, with a range sensitivity of one part in 1000 being typical for this approach. A low-cost passive range metrology system is described based on geometrical imaging with distance measurement sensitivity to better than one part in 10,000. The approach uses knowledge of the relationship between features on the target and the imaging parameters of the metrology camera, as in the parallax/centroid approach, but incorporates a specific target encoding that optimizes the performance. Results are presented using a standard machine vision camera in room ambient lighting conditions, showing a range sensitivity of 100 microns with a target-camera separation of 1200 mm.
Dual-illumination NIR system for wafer level defect inspection
CdZnTe is a high efficiency, room temperature radiation detection material that has attracted great interesting in medical and security applications. CZT crystals can be grown by various methods. Particularly, CZT grown with the Transfer Heater Method (THM) method have been shown to have fewer defects and greater material uniformity. In this work, we developed a proof-of-concept dual lighting NIR imaging system that can be implemented to quickly and nondestructively screen CZT boule and wafers during the manufacturing process. The system works by imaging the defects inside CZT at a shallow depth of focus, taking a stack of images step by step at different depths through the sample. The images are then processed with in-house software, which can locate the defects at different depths, construct the 3D mapping of the defects, and provide statistical defect information. This can help with screening materials for use in detector manufacturing at an early stage, which can significantly reduce the downstream cost of detector fabrication. This inspection method can also be used to help the manufacturer understand the cause of the defect formation and ultimately improve the manufacturing process.
Poster Session
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Alignment and integration of ASSIST: a test bench for VLT adaptive optics facility
Atul Deep, Robin Arsenault, Wilfried Boland, et al.
ASSIST, The Adaptive Secondary Setup and Instrument STimulator, is being developed to provide a testing facility for the ESO Adaptive Optics Facility (AOF). It will allow the off-telescope testing of three elements of the VLT AOF; the Deformable Secondary Mirror (DSM) and the AO systems for MUSE and HAWK-I (GALACSI and GRAAL). The core of ASSIST consists of a 2-mirror setup (AM1-AM2) allowing the on-axis test of the DSM in interferometric mode. However, during the initial stages of ASSIST integration, DSM would not be present. This makes the task of aligning AM1-AM2 to within an accuracy of 0.05mm/1 arcmin rather challenging. A novel technique known as Shack-Hartmann method has been developed and tested in the lab for this purpose. A Shack Hartmann wavefront sensor will be used to measure the mis-alignment between AM1-AM2 by recording the coma and astigmatism in the presence of large spherical aberration introduced because of tilt/decenter of AM2 with respect to AM1. Thereafter, 20 optical components including lenses, flat mirrors and beam-splitter cubes divided into five sub-assemblies should be aligned to AM1-AM2- DSM axis which ultimately passes through the mechanical axis of large AMOS rotator.
Scattering in random profiling surfaces
We use the profile of a parabolic mirror to calculate the scattered electromagnetic field, this mirror can be used in the design and construction of a reflector telescope. We calculate the effect caused by the roughness on the performance of this optical elements, the calculation is done within the Rayleigh approximation. In another work presented in this meeting we show a comparison of the results obtained numerically using different roughness parameters and calculate its effect on the aberrations of the wavefront.
Cost and performance trade-offs for commercially available linear stages
Katie Schwertz, J. H. Burge
The following paper provides the practicing engineer with guidelines on the relationships between cost and various performance factors for different types of linear stages. When multiple precise motions need to be made in a system, stages are typically the solution. A number of factors should be considered before choosing a stage: cost, load capacity, travel range, repeatability, resolution, encoding accuracy, errors in motion, stiffness, stability, velocity of motion, environmental sensitivity, and additional features like over-travel protection and locking mechanisms. There are a variety of different bearing types for linear stages, each with their own advantages and disadvantages. This paper presents charts that provide relationships between the cost, travel range, angular deviation, and load capacity of various types of manual one-axis linear stages. The stages considered were those that had less than a 2.5" travel range and sold by major optomechanical vendors. The bearing types investigated were dovetail, flexure, ball bearing, double row ball bearing, crossed roller bearing, and gothic arch ball bearing. Using the charts and general guidelines provided in this paper, a more informed decision may be made when selecting a linear stage.