This PDF file contains the front matter associated with SPIE Proceedings Volume 6692, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

To take advantage of the unique environment of space and optimize infrared observations for faint sources, space telescopes must be cooled to low temperatures. The new paradigm in cooling large space telescopes is to use a combination of passive radiative cooling and mechanical cryocoolers. The passive system must shield the telescope from the Sun, Earth, and the warm spacecraft components while providing radiative cooling to deep space. This shield system is larger than the telescope itself, and must attenuate the incoming energy by over one million to limit heat input to the telescope. Testing of such a system on the ground is a daunting task due to the size of the thermal/vacuum chamber required and the degree of thermal isolation necessary between the room temperature and cryogenic parts of the shield. These problems have been attacked in two ways: by designing a subscale version of a larger sunshield and by carefully closing out radiation sneak paths. The 18% scale (the largest diameter shield was 1.5 m) version of the SPIRIT Origins Probe telescope shield was tested in a low cost helium shroud within a 3.1 m diameter x 4.6 m long LN₂ shrouded vacuum chamber. Thermal straps connected from three shield stages to the liquid helium cooled shroud were instrumented with heaters and thermometers to simulate mechanical cryocooler stages at 6 K, 18-20 K, and 45-51 K. Performance data showed that less than 10 microwatts of radiative heat leaked from the warm to cold sides of the shields during the test. The excellent agreement between the data and the thermal models is discussed along with shroud construction techniques.

In order to enable high quality lens designs using calcium fluoride (CaF₂) and Heraeus Infrasil 301 (Infrasil) for cryogenic operating temperatures, we have measured the absolute refractive index of these two materials as a function of both wavelength and temperature using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center. For CaF₂, we report absolute refractive index and thermo-optic coefficient (dn/dT) at temperatures ranging from 25 to 300 K at wavelengths from 0.4 to 5.6 μm, while for Infrasil, we cover temperatures ranging from 35 to 300 K and wavelengths from 0.4 to 3.6 μm. For CaF₂, we compare our index measurements to measurements of other investigators. For Infrasil, we compare our measurements to the material manufacturer's data at room temperature and to cryogenic measurements for fused silica from previous investigations including one of our own. Finally, we provide temperature-dependent Sellmeier coefficients based on our measured data to allow accurate interpolation of index to other wavelengths and temperatures.

In order to enable high quality lens designs using N-BK7, BaLKN3, SF15, and E-SF03 at cryogenic temperatures, we have measured the absolute refractive index of prisms of these four materials using the Cryogenic, High-Accuracy Refraction Measuring System (CHARMS) at NASA's Goddard Space Flight Center, as a function of both wavelength and temperature. For N-BK7, we report absolute refractive index and thermo-optic coefficient (dn/dT) at temperatures ranging from 50 to 300 K at wavelengths from 0.45 to 2.7 μm; for BaLKN3 we cover temperatures ranging from 40 to 300 K and wavelengths from 0.4 to 2.6 μm; for SF15 we cover temperatures ranging from 50 to 300 K and wavelengths from 0.45 to 2.6 μm; for E-SF03 we cover temperatures ranging from 30 to 300 K and wavelengths from 0.45 to 2.8 μm. We compare our measurements with others in the literature and provide temperature-dependent Sellmeier coefficients based on our data to allow accurate interpolation of index to other wavelengths and temperatures. While we generally find good agreement (+/-2 x 10^-4 for N-BK7, +/-4 x 10^-4 for E-SF03, <1x10^-4 for the other materials) at room temperature between our measured values and those provided by the vendor, there is some variation between the datasheets provided with the prisms we measured and the catalog values published by the vendor. This underlines the importance of measuring the absolute refractive index of the material when precise knowledge of the refractive index is required.

These studies consist of measuring the frequency dependent transmittance (T(ω)) and reflectance (R(ω)) above and below the optical band-gap in the UV/Visible and infrared frequency ranges for Cd_1-xZn_xTe materials for x=0 and x=0.04. Measurements were also done in the temperature range from 5 to 300 K. The results show that the optical gap near 1.49 eV at 300 K increases to 1.62 eV at 5 K. Finally, we observe sharp absorption peaks near this gap energy at low temperatures for the x=0.04 sample. The close proximity of these peaks to the optical transition threshold suggests that they originate from the creation of bound electron-hole pairs or excitons. The decay of these excitonic absorptions may contribute to a photoluminescence and transient background response of these back-illuminated HgCdTe CCD detectors.

This report describes the facility, experimental methods, characterizations, and uncertainty analysis of the Cryo- Distortion Measurement Facility (CDMF) at the Goddard Space Flight Center (GSFC). This facility is designed to measure thermal distortions of structural elements as the temperature is lowered from 320K to below 40 K over multiple cycles, and is capable of unattended running and data logging. The first measurement is the change in length and any bending of composite tubes with Invar end-fittings. The CDMF includes a chamber that is efficiently cooled with two cryo-coolers (one single-stage and one two-stage) rather than with liquid cryogens. Five optical ports incorporate sapphire radiation shields - transparent to the interferometer - on each of two shrouds and a fused silica vacuum-port window. The change in length of composite tubes is monitored continuously with displacement-measuring interferometers; and the rotations, bending, and twisting are measured intermittently with theodolites and a surface-figure interferometer. Nickel-coated invar mirrors and attachment mechanisms were developed and qualified by test in the CDMF. The uncertainty in measurement of length change of 0.4 m tubes is currently estimated at 0.9 micrometers.

The Lockheed Martin - University of Arizona Infrared Spectrometer (LAIRS) is designed to image the emission lines of celestial objects in the 1.3-2.5 μm regime. The Instrument has been built and tested at the Lockheed Martin Space Systems Advanced Technology Center, and demonstrated to work at cryogenic temperatures. The Instrument employs a tunable Fabry-Perot Interferometer (FPI) to select the wavelength at which the Instrument images targets. The FPI employs voice coil actuators and capacitive sensors to maintain parallelism of its reflective lenses and control their gap spacing. During functional tests of the FPI and the LAIRS instrument, finesse numbers of 60 and 24 were measured for the interferometer at room temperature and 80K, respectively. This measurement was performed using a laser operating at 1529.33 nm. This paper presents an overview of the optical, mechanical, and control design of the FPI, as well as a summary of cryogenic test results.

A cryogenic Fourier transform infrared spectrometer (Cryo-FTS) was developed for the Low Background Infrared (LBIR) facility at the National Institute of Standards and Technology (NIST). This spectrometer was developed for the Missile Defense Agency Transfer Radiometer (MDXR) that will be used to calibrate infrared sources that can not be transported to NIST for calibration. When used inside the MDXR, the Cryo-FTS is expected to be able to provide relative spectral measurements with an accuracy of < 0.3 % uncertainty of infrared sources with a spectral range from 4μm to 15 μm and a spectral resolution of 0.6 cm^-1. The Cryo-FTS spectral range is determined by the beamsplitter since all of its other optics use reflective materials. The compact interferometer uses a compensated Michelson configuration and has an operating temperature range between 10 K and 340 K with very low static beam redirection (< 215 μrad). The interferometer uses flat metal mirrors and KBr flat optics and maintains low wavefront distortion for infrared beams of up to 1.63 cm diameter. It integrates a digitally servo-controlled porchswing mechanism to provide an accurate and repeatable optical path difference and is supported by a Wavefront Alignment (WA) system to correct for wavefront residual tilt in real time using a fibre optic based metrology system. The interferometer is expected to provide modulation efficiency of better than 22% with limited power dissipation (< 2.8 W) during continuous operation.

TNO has developed a compact BreadBoard (BB) cryogenic Optical Delay Line (ODL) for use in future space interferometry missions such as ESA's Darwin and NASA's TPF-I. The breadboard delay line is representative of a flight mechanism. The optical design is a two-mirror cat's-eye. A linear guiding system based on magnetic bearings provides frictionless and wear free operation with zero hysteresis. The delay line has a voice coil actuator for single stage Optical Path Difference (OPD) control. The verification program, including functional testing at 40 K, has been completed succesfully.

MIDIR is the proposed thermal/mid-IR imager and spectrograph for the European Extremely Large Telescope (E-ELT). It will cover the wavelength range of 3 to at least 20 μm. Designed for diffraction-limited performance over the entire wavelength range, MIDIR will require an adaptive optics system; a cryogenically cooled system could offer optimal performance in the IR, and this is a critical aspect of the instrument design. We present here an overview of the project, including a discussion of MIDIR's science goals and a comparison with other infrared (IR) facilities planned in the next decade; top level requirements derived from these goals are outlined. We describe the optical and mechanical design work carried out in the context of a conceptual design study, and discuss some important issues to emerge from this work, related to the design, operation and calibration of the instrument. The impact of telescope optical design choices on the requirements for the MIDIR instrument is demonstrated.

The Near Infrared Camera (NIRCam) instrument for NASA's James Webb Space Telescope (JWST) has an optical prescription which employs several mirrors, some of which are powered and some of which are flats that aid in packaging. Two distinct designs for the mirrors and their mounts have been developed such that different requirements for mass, packaging and induced wavefront error can be met. The instrument will operate at 37K after experiencing launch loads at ~293K and the mounts must accommodate all associated thermal and mechanical stresses. Two of the mirrors needed to be redesigned after initial prototype testing of one of the designs. This paper will provide an update on the design and analysis status for all the mirrors including results of the initial prototype testing.

An example is given of how cryogenic optical testing is being performed for the NIRCam instrument. A 94 mm diameter Lithium Fluoride lens was mounted and thermally cycled between room temperature and approximately 60 K. Interferometric measurements were taken before, during, and after the cycling to determine the effects of temperature on the optical performance. We found that the net distortion of the surface of the lens decreased with temperature. We also found that that the distortion did not increase as the temperature rose again, and that the transmitted wavefront quality remained unchanged before and after thermal cycling.

The Dichroic Beam Splitter (DBS) in the NIRCam instrument is required to have small reflected wavefront error and high throughput in order for the instrument to view the images of first light in the Universe in the James Webb Space Telescope (JWST). The operating temperature of the instrument is from 32 Kelvin to 39.5 Kelvin. We have performed NIRCam prototype DBS (fabricated by JDS Uniphase) spectral and reflected wavefront error measurements at cryogenic temperatures. We report the experiment and the results in this paper.

Single crystal Lithium Fluoride has been base-lined as one of the optical materials for the Near Infra-Red Camera (NIRCam) on the James Webb Space Telescope (JWST). Optically, this material is outstanding for use in the near IR. Unfortunately, this material has poor mechanical properties, which make it very difficult for use in any appreciable size on cryogenic space based instruments. In addition to a dL/L from 300K to 30K of ~-0.48%, and a room temperature CTE of ~37ppm/K, the material deforms plastically under relatively small tensile loading. This paper will update a paper presented in 2005 on the same optical mount [1]. The mount has been proven via vibration and thermal-vacuum testing to successfully mount large (70 mm-94 mm) Lithium Fluoride optics for application in space. An overview of Lithium Fluoride material properties and characteristics is given and updated yield strength test data is provided and discussed. A design limit load is determined for the material based on strength values from the literature as well as independent testing. The second generation mount design is then presented along with test data and results. Finally, the test results are discussed showing survival and performance of the optic and mount during cool-down to the operational thermal environment.

The Near Infrared Camera (NIRCam) instrument for NASA's James Webb Space Telescope (JWST) is one of the four science instruments to be installed into the Integrated Science Instrument Module (ISIM) on JWST. NIRCam's requirements include operation at 37 Kelvin to produce high resolution images in two wave bands encompassing the range from 0.6 microns to 5 microns. In addition, NIRCam is to be used as a metrology instrument during the JWST observatory commissioning on orbit, during the precise alignment of the observatory's multiple-segment primary mirror. This paper will provide an update to the NIRCam Thermal subsystem design for stable operation at 37 Kelvin.

MIRI ('Mid Infrared Instrument') is the combined imager and integral field spectrometer for the 5-29 micron wavelength range under development for the JWST. In March 2007 the qualification and verification phase of the Spectrometer Main Optics (SMO), part of the MIRI spectrometer came to an end. In this phase it is shown that the SMO subsystem can provide the necessary performance and withstand the harsh environments of a launch and outer space. In this phase different models of the SMO have been inspected with respect to performance parameters like alignment and image quality and have been exposed to vibration tests and successive cryogenic cool downs. This paper will describe the philosophy behind the verification plan, the chosen test strategy and reports the results of these tests. In addition the paper covers the design of the optical test setup, focusing on the simulation of the optical interfaces of the SMO.

The MTS Folding Mirror Subsystem is part of the MIRI Telescope Simulator, which is an Optical Ground Support Equipment for ESA MIRI (Medium Infrared Instrument) Qualification, in the frame of the James Webb Space Telescope Program. The program prime contractor is INTA (Spanish National Aerospace Centre). The Subsystem consists of four different mirrors assemblies to adapt the optical path to the available envelope; the mirrors are placed between exit pupil and image plane with suitable orientation to reproduce specific chief ray deviation. Remote adjustment for image compensation at cryogenic conditions is available for two mirror assemblies, by means of two independent rotation mechanisms. A manual tip-tilt system is also provided for system adjusting at ambient conditions in all four mirror assemblies.

The James Webb Space Telescope (JWST) mission is a collaborative project between the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA) and the Canadian Space Agency (CSA). JWST is considered the successor to the Hubble Space Telescope (HST) and although its design and science objectives are quite different, JWST is expected to yield equivalently astonishing breakthroughs in infrared space science. Due to be launched in 2013 from the French Guiana, the JWST observatory will be placed in an orbit around the anti- Sun Earth-Sun Lagrangian point, L2, by an Ariane 5 launcher, provided by ESA. The payload on board the JWST observatory consists of four main scientific instruments: a near-infrared camera (NIRCam), a combined mid-infrared camera/spectrograph (MIRI), a near-infrared tunable filter (TFI) and a nearinfrared spectrograph (NIRSpec). The instrument suite is completed by a Fine Guidance Sensor (FGS). Besides the provision of the Ariane 5 launcher, ESA, with EADS Astrium GmbH (D) as Prime Contractor, is fully responsible for the funding and the furnishing of NIRSpec and, at the same time, for approximately half of MIRI costs through special contributions from the ESA member states. NIRSpec is a multi-object, spectrograph capable of measuring the spectra of about 100 objects simultaneously at low (R=100), medium (R=1000), and high (R=2700) resolutions over the wavelength range between 0.6 micron and 5.0 micron. In this article we provide a general overview of its main design features and performances.

The James Webb Space Telescope (JWST) Observatory, the follow-on mission to the Hubble Space Telescope, will yield astonishing breakthroughs in infrared space science. One of the four instruments on that mission, the NIRSpec instrument, is being developed by the European Space Agency with EADS Astrium Germany GmbH as the prime contractor. This multi-object spectrograph is capable of measuring the near infrared spectrum of at least 100 objects simultaneously at various spectral resolutions in the 0.6 μm to 5.0 μm wavelength range. A physical optical model, based on Fourier Optics, was developed in order to simulate some of the key optical performances of NIRSpec. Realistic WFE maps were established for both the JWST optical telescope as well as for the various NIRSpec optical stages. The model simulates the optical performance of NIRSpec at the key optical pupil and image planes. Using this core optical simulation module, the model was expanded to a full instrument performance simulator that can be used to simulate the response of NIRSpec to any given optical input. The program will be of great use during the planning and evaluation of performance testing and calibration measurements.

The James Webb Space Telescope (JWST) is a 6.6m diameter, segmented, deployable telescope for cryogenic IR space astronomy (~40K). 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 ISIM structure must meet its requirements at the ~40K cryogenic operating temperature. 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 for stress relief and in order to measure temperature-induced mechanical, structural changes. These ambient-to-cryogenic changes in the alignment of SI and OTE-related interfaces are an important component in the JWST Observatory alignment plan and must be verified. We report on the planning for and preliminary testing of a cryogenic metrology system for ISIM based on photogrammetry. Photogrammetry is the measurement of the location of custom targets via triangulation using images obtained at a suite of digital camera locations and orientations. We describe metrology system requirements, plans, and ambient photogrammetric measurements of a mock-up of the ISIM structure to design targeting and obtain resolution estimates. We compare these measurements with those taken from a well known ambient metrology system, namely, the Leica laser tracker system.

Dome seeing, one of the most important problems in LAMOST due to its special optical path, mainly depends on thermal distribution and temperature gradients in the enclosure. It is necessary to compute and then control the thermal distribution inside the enclosure. The paper puts up many thermal analysis models with Icepak software, calculates their thermal distribution under different thermal cases, and analyzes the maximal temperature differences in different cross sections along the optical path. We apply many cooling methods, which include adding openings, forming ventilation, forcing convection and local cooling. We also take the maximal temperature difference as an optimization object to control the thermal distribution and optimize the cooling structure. Computation results demonstrate that improving the thermal distribution can greatly reduce the temperature gradient. Through analysis we have obtained one cooling method that involves a specific ventilating duct forming local cooling and intake cooling air. Simulation shows the maximal temperature difference has been decreased from 3.8°C to 0.8640°C and in every cross section the maximal temperature gradient has reached 0.125°C/m, which is better than the project demand of 0.4°C/m. All results confirm the thermal control system of this project.

The James Webb Space Telescope's (JWST) Integrated Science Instrument Module (ISIM) contains the observatory's four science instruments and their support subsystems. During alignment and test of the integrated ISIM at NASA's Goddard Space Flight Center (GSFC), the Optical telescope element SIMulator (OSIM) will be used to optically stimulate the science instruments to verify their operation and performance. In this paper we present the design of two cryogenic alignment fixtures that will be used to align the OSIM to the ISIM during testing at GSFC. These fixtures, the Master Alignment Target Fixture (MATF) and the ISIM Alignment Target Fixture (IATF), will provide continuous, six degree of freedom feedback to OSIM during initial ambient alignment as well as during cryogenic vacuum testing. These fixtures will allow us to position the OSIM and detect OSIM-ISIM absolute alignment to better than 180 microns in translation and 540 micro-radians in rotation. We will provide a brief overview of the OSIM system and we will also discuss the relevance of these fixtures in the context of the overall ISIM alignment and test plan.

The James Webb Space Telescope (JWST) has among its challenges the minimization of the effects of ice on its optical performance in terms of transmission. The ice is a result of JWST's architecture, mission design and materials selection. The optical properties of ice are introduced to illustrate why there is concern among JWST's designers about ice build up. Several alternate methods of determining the impact on mirror reflectance are compared. Two are derived from Beer's Law and the third is full thin film treatment. It is shown and argued that only the thin film method captures enough of the physics of interaction of the incident light with an ice coated mirror.