Ball Aerospace & Technologies Corp. (BATC) has added a powerful capability to its existing imaging spectrometer
alignment and test facilities: Scanning Fabry-Perot source filters. These interferometers provide a means for efficient
instrument testing with full characterization from the ultra-violet (UV) to longwave infrared (LWIR). Spectral Response
Functions (SRF) and geometric distortions are accurately determined with a common approach. The techniques were
demonstrated with a two band cryogenic LWIR spectrometer and with the mid-wave infrared (MWIR) Spaceborne
InfraRed Atmospheric Sounder for Geosynchronous Earth Orbit (SIRAS-G) laboratory demonstration imaging
spectrometer. The spectrometer testing and performance is presented.
The Spaceborne Infrared Sounder for Geosynchronous Earth Orbit (SIRAS-G) was developed by Ball Aerospace and
Technologies Corp (BATC) under NASA's 2002 Instrument Incubator Program. SIRAS-G is a technology development
program focused on next-generation IR imaging spectrometers for sounding of the atmosphere. SIRAS-G is ideally
suited for measuring atmospheric temperature and water vapor profiles, trace gases concentrations, land and ocean
surface temperatures and the IR mineral dust aerosol signature from satellite, providing high-spectral resolution imaging
spectroscopy over a broad IR spectral range and extended field of view. Instrument concepts for future mission in LEO
and GEO are discussed, including an instrument concept to be flown in low earth orbit having the potential to provide
high spatial resolution, comparable to that of MODIS, along with the high spectral resolution currently being
demonstrated by the Atmospheric Infrared Sounder (AIRS). This capability would dramatically improve the yield of
cloud-free pixels scenes that can be assimilated into Numerical Weather Prediction (NWP) models. The SIRAS-G
dispersive spectrometer module is readily adaptable for missions in LEO, GEO and MEO orbits and can be optimized
for spectral resolution over subsets of the total spectral range. We have completed the 3-year SIRAS-G IIP development
effort, including successful testing of the SIRAS-G laboratory demonstration spectrometer that utilized the Hawaii 1RG
MWIR FPA. Performance testing was conducted at cryogenic temperatures and the performance of the demo instrument
has been quantified including measurement of keystone distortion, spectral smile, MTF, and the spectral response
function (SRF) to high accuracy. We present the results of the laboratory instrument development including
characterization of the demonstration instrument performance. We discuss instrument concepts utilizing SIRAS-G
technology for potential future missions including an anticipated airborne flight demonstration.
The Spaceborne Infrared Atmospheric Sounder for Geosynchronous Earth Orbit (SIRAS-G) is an infrared imaging spectrometer concept being developed to address future Earth observation from both low-earth and geosynchronous orbit. SIRAS-G is now in its second year of development as part of NASA's Instrument Incubator Program. The SIRAS-G approach offers lower mass and power requirements than heritage instruments while offering enhanced capabilities for measuring atmospheric temperature, water vapor, and trace gas column abundances at improved spatial resolution. The system employs a wide field-of-view hyperspectral infrared optical system that splits the incoming radiation to several grating spectrometer channels. Combined with large 2-D focal planes, this system provides for simultaneous spectral and high-resolution spatial imaging. In 1999, the SIRAS team built and tested the SIRAS LWIR spectrometer also under NASA's Instrument Incubator Program (IIP-1). SIRAS-G builds on this experience with a goal of producing a laboratory demonstration instrument operating in the MWIR including the telescope, a single spectrometer channel, focal plane and active cooling subsystem. In this paper, we describe the on-going development of this instrument concept, focusing on aspects of the optical design, fabrication and testing of the demonstration instrument, performance requirement predictions and potential future scientific instrument applications.
The standard aspheric surface, a conic surface figured with a polynomial expansion, provides excellent correction in many optical design problems. But there are problems where this set of basis functions does not provide the best solution. This paper discusses a parametric curve alternative called Non-Uniform Rational B-Splines (NURBS). NURBS are used extensively in the computer aided geometric design industry (CAGD) because they offer a rational segmented polynomial curve with the flexibility of setting both the order of the B-spline segments and the locations of the knots, or joints, between the B-spline segments providing local curve control. In addition, they are numerically stable and they have geometric intuitive control points for manipulating the curve. The advantages and disadvantages of using NURBS in optical design applications are discussed. Brief explanations of NURBS curve mathematics, properties, and design techniques are presented. The paper concludes with an optical design example comparing the optical performance between rotationally symmetric NURBS surfaces and standard aspheric surface. Note that all of the aspheric surfaces discussed in this paper are rotationally symmetric.
We report prototype active-matrix liquid crystal spatial light modulators using ordinary silicon integrated-circuit backplanes and incorporating a fast-switching ferroelectric liquid crystal light modulating layer at the backplane's surface. Backplanes reported here utilize a fully- planarized three-metal CMOS process for improved optical throughput, contrast, and light tolerance. We report a 256 X 256 device with 15 micrometers SRAM pixels having 87% fill- factor, optical throughput of 36 - 45%, contrast ratio of 80:1, and electrical rise/fall times of 85 microsecond(s) . We also report DRAM arrays with pixel pitches of 7.5 micrometers and 5.7 micrometers , with fill factors of 75% and 69%, respectively.
We have made 128 X 128 and 256 X 256 spatial light modulators using active backplanes fabricated through a commodity silicon foundry and incorporating a thin ferroelectric liquid crystal light modulating layer at the backplane's surface by means of postprocessing of individual foundry die. These electrically addressed devices exhibit optical rise and fall times as short as 105 microsecond(s) , with contrast ratios in images as high as 100:1, and in zero-order diffracted light as high as 200:1. Total optical throughput to the zero-order diffracted beam exceeds 10% for the 256 X 256 devices and 17% for the 128 X 128 devices. Frame update times shorter than 100 microsecond(s) , corresponding to image information throughput of greater than 80 MBytes/s, were realized by employing pipelining techniques in conjunction with a wide digital input word.