ABSTRACT
We present the design, implementation, and on-ground performance measurements of the Ionospheric Connection Explorer EUV spectrometer, ICON EUV, a wide field (17° x 12°) extreme ultraviolet (EUV) imaging spectrograph designed to observe the lower ionosphere at tangent altitudes between 100 and 500 km. The primary targets of the spectrometer, which has a spectral range of 54-88 nm, are the Oil emission lines at 61.6 nm and 83.4 nm. Its design, using a single optical element, permits a 0°.26 imaging resolution perpendicular to the spectral dispersion direction with a large (12°) acceptance parallel to the dispersion direction while providing a slit-width dominated spectral resolution of R ~ 25 at 58.4 nm. Pre-flight calibration shows that the instrument has met all of the science performance requirements.
ABSTRACT
Retrievals of atmospheric composition from near-infrared measurements require measurements of airmass to better than the desired precision of the composition. The oxygen bands are obvious choices to quantify airmass since the mixing ratio of oxygen is fixed over the full range of atmospheric conditions. The OCO-2 mission is currently retrieving carbon dioxide concentration using the oxygen A-band for airmass normalization. The 0.25% accuracy desired for the carbon dioxide concentration has pushed the required state-of-the-art for oxygen spectroscopy. To measure O2 A-band cross-sections with such accuracy through the full range of atmospheric pressure requires a sophisticated line-shape model (Rautian or Speed-Dependent Voigt) with line mixing (LM) and collision induced absorption (CIA). Models of each of these phenomena exist, however, this work presents an integrated self-consistent model developed to ensure the best accuracy. It is also important to consider multiple sources of spectroscopic data for such a study in order to improve the dynamic range of the model and to minimize effects of instrumentation and associated systematic errors. The techniques of Fourier Transform Spectroscopy (FTS) and Cavity Ring-Down Spectroscopy (CRDS) allow complimentary information for such an analysis. We utilize multispectrum fitting software to generate a comprehensive new database with improved accuracy based on these datasets. The extensive information will be made available as a multi-dimensional cross-section (ABSCO) table and the parameterization will be offered for inclusion in the HITRANonline database.
ABSTRACT
A simple method for determining the focal ratio degradation of optical fibers has been developed. The method involves splitting the light from the test fiber and recording ring patterns that have traveled over two different, and known, optical paths. This new method will be valuable for testing many fibers as will be needed for new multiobject astronomical spectrographs.
ABSTRACT
We have developed and tested an antireflection (AR) coating method for silicon lenses used at cryogenic temperatures and millimeter wavelengths. Our particular application is a measurement of the cosmic microwave background. The coating consists of machined pieces of Cirlex glued to the silicon. The measured reflection from an AR-coated flat piece is less than 1.5% at the design wavelength. The coating has been applied to flats and lenses and has survived multiple thermal cycles from 300 to 4 K. We present the manufacturing method, the material properties, the tests performed, and estimates of the loss that can be achieved in practical lenses.
