The LOng-Range Reconnaissance Imager (LORRI) is a panchromatic imager for the New Horizons Pluto/Kuiper belt mission. New Horizons is being prepared for launch in January 2006 as the inaugural mission in NASA's New Frontiers program. This paper discusses the calibration and characterization of LORRI.
LORRI consists of a Ritchey-Chretien telescope and CCD detector. It provides a narrow field of view (0.29°), high resolution (pixel FOV = 5 μrad) image at f/12.6 with a 20.8~cm diameter primary mirror. The image is acquired with a 1024 x 1024 pixel CCD detector (model CCD 47-20 from E2V). LORRI was calibrated in vacuum at three temperatures covering the extremes of its operating range (-100°C to +40°C for various parts of the system) and its predicted nominal temperature in-flight. A high pressure xenon arc lamp, selected for its solar-like spectrum, provided the light source for the calibration. The lamp was fiber-optically coupled into the vacuum chamber and monitored by a calibrated photodiode. Neutral density and bandpass filters controlled source intensity and provided measurements of the wavelength dependence of LORRI's performance. This paper will describe the calibration facility and design, as well as summarize the results on point spread function, flat field, radiometric response, detector noise, and focus stability over the operating temperature range.
LORRI was designed and fabricated by a combined effort of The Johns Hopkins University Applied Physics Laboratory (APL) and SSG Precision Optronics.
Calibration was conducted at the Diffraction Grating Evaluation Facility at NASA/Goddard Space Flight Center with additional characterization measurements at APL.
The complex study of a ultra-fine (4000 to 5870 grooves/mm) holographic gratings designed for Near Ultra Violet (NUV) channel of Cosmic Origin Spectrograph (COS) are presented. The gratings underwent a comprehensive program of efficiency and scatter characterization at flight-like environment conditions. Initial tests revealed significant departures of grating efficiencies from the values predicted. Effects of profile non-replication (layers nonconformity) for multi-layer coated grating surfaces are investigated. The rigorous efficiency modeling based on groove profiling atomic force microscopy (AFM) data for both multi-layer conformal and non-conformal coated gratings in both polarizations
allowed to identify the problem as a leaky mode anomalies for dielectrically coated gratings. Both shift in peak efficiencies and wide absorption band are observed to be critically dependant of grating groove shape and reflective coating thickness. Grating depth/profile topography changes induced by coating process are observed and called for groove profile measurements at all stages of the gratings production line. Grating scatter characterizations data for COS and SORCE/SOLSTICE gratings at UV-VUV wavelength are presented. The wavelength scaling at VUV-UV waveband (140 nm to 442 nm) for holographically ruled 3600 gr/mm grating are also reported.
Design and performance of Fully Automated Ultraviolet Spectrographic Tester (FAUST) providing Bidirectional Scatter Distribution Function (BSDF) measurements at wavelengths ranging from the vacuum ultraviolet to the infrared has been described in details. The instrument is capable of measuring both very near (3 arcseconds) and very wide angle (over 120 degrees) scatter off both highly specular (mirrors and gratings) and highly diffuse surfaces for +/- 90 degrees incidence angle variations. Scatterometer dynamic range of over 11 orders of magnitude has been demonstrated. Stray light reduction techniques practicing for instrument signature improvement are discussed. Principles of light sources and detectors choice, instrument automation and calibration are explained. Instrument signature data along with some examples of a list of scatter measurements and gratings efficiency measurements performed by the use of FAUST are also presented here.
Methods for surface metrology have advanced significantly in the last few years, driven largely by the metrology needs for advanced lithographic processes. This paper applies recently developed metrology techniques to the specific problem of determining the groove structure of diffraction gratings well enough to reliably predict performance. Metrology devices used include an atomic force microscope, a contact profilometer, and a late-model optical microinterferometer. Examples of shallow (far-UV, high dispersion) and deep (IR echelle) gratings are presented, along with some conclusions of which metrology techniques are applicable for which types of diffraction grating. Also required along with the metrology is the use of fast, full electromagnetic model efficiency calculation codes which calculate the efficiency to be expected from a given mount, materials set, and grating profile. We present results qualifying codes we use against known and published results.
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