Calcium fluoride is a desirable material for optical design of space systems in the ultraviolet, visible, and infrared bands. Modern calcium fluoride materials fabricated for the photolithography industry are highly resistant to space radiation. The wide wavelength band and low dispersion are also desirable properties. Unfortunately, calcium fluoride has a host of significant material property issues which hinder its use in the space environment. Low hardness, susceptibility to thermal and mechanical shock, and large coefficient of thermal expansion present significant challenges during development of opto-mechanical designs. Sandia National Laboratories Monitoring Systems and Technology Center has fielded a calcium fluoride based optical system for use in space. The Sandia design solution is based upon a spring-loaded mount which uses no volatile organic compounds. The theory of the Sandia solution is developed and design rules are presented. The Sandia design solution is illustrated for a specific example. Example design and margin calculations are shown. Finally, lessons learned from our design realization and qualification testing efforts are shared for the benefit of the community.
KEYWORDS: Error analysis, Tolerancing, Received signal strength, Monte Carlo methods, LCDs, Computer aided design, Assembly tolerances, Statistical analysis, Telescopes, Headlamps
Two-Axis Rotation Systems, or “goniometers,” are used in diverse applications including telescope pointing, automotive headlamp testing, and display testing. There are three basic configurations in which a goniometer can be built depending on the orientation and order of the stages. Each configuration has a governing set of equations which convert motion between the system “native” coordinates to other base systems, such as direction cosines, optical field angles, or spherical-polar coordinates. In their simplest form, these equations neglect errors present in real systems. In this paper, a statistical treatment of error source propagation is developed which uses only tolerance data, such as can be obtained from the system mechanical drawings prior to fabrication. It is shown that certain error sources are fully correctable, partially correctable, or uncorrectable, depending upon the goniometer configuration and zeroing technique. The system error budget can be described by a root-sum-of-squares technique with weighting factors describing the sensitivity of each error source. This paper tabulates weighting factors at 67% (k=1) and 95% (k=2) confidence for various levels of maximum travel for each goniometer configuration. As a practical example, this paper works through an error budget used for the procurement of a system at Sandia National Laboratories.
A familiar concept in imaging spectrometry is that of the three dimensional data cube, with one spectral and two spatial dimensions. However, available detectors have at most two dimensions, which generally leads to the introduction of either scanning or multiplexing techniques for imaging spectrometers. For situations in which noise increases less rapidly than as the square root of the signal, multiplexing techniques have the potential to provide superior signal-to-noise ratios. This paper presents a theoretical description and numerical simulations for a new and simple type of Hadamard transform multiplexed imaging spectrometer. Compared to previous types of spatially encoded imaging spectrometers, it increases etendue by eliminating the need for anamorphically compressed re-imaging onto the entrance aperture of a monochromator or spectrophotometer. Compared to previous types of spectrally encoded imaging spectrometers, it increases end-to-end transmittance by eliminating the need for spectral re-combining optics. These simplifications are attained by treating the pixels of a digital mirror array as virtual entrance slits and the pixels of a 2-D array detector as virtual exit slits of an imaging spectrometer, and by applying a novel signal processing technique.
With the number of cerium doped radiation resistant glasses available to the designer of space optics rapidly decreasing, it is critical to identify and characterize all potential sources of radiation resistant glasses and crystals. Unfortunately much of the data on radiation testing of glasses is quite old and often not completed at very high dose rates as might be experienced by an unshielded space optic in orbit for many years. In addition, many optical glasses and crystals are manufactured today with much higher purity than in the past in order to increase their ultraviolet transmission properties. Consequently these glasses are much more resistant to space radiation than in the past. In this paper we will present gamma radiation effects on the transmission properties of today's fused silica, sapphire, calcium fluoride, barium fluoride, Schott cerium doped radiation resistant glasses, Schott colored glass filters, as well as some infrared glasses with up to a 10 Mrad dose.
Thermal imaging systems that are used in quantitative applications such as pyrometry or pulsed thermography must be calibrated to provide accurate and repeatable measurements. Several approaches are possible ranging from simple linear calibration to the characterization of detector response using polynomial relationships. This paper describes the application of these calibration techniques to a thermal imaging microscope that must operate over a broad, rapidly changing temperature range while remaining sensitive to small variations in surface temperature. Such an application requires the ability to change the infrared camera exposure and associated calibration parameters quickly. It also requires a method to compensate for variations in background thermal radiance due to the optical configuration of a thermal imaging microscope.
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