Silicon and germanium are perhaps the two most well-understood semiconductor materials in the context of solid state device technologies and more recently micromachining and nanotechnology. Meanwhile, these two materials are also important in the field of infrared lens design. Optical instruments designed for the wavelength range where these two materials are transmissive achieve best performance when cooled to cryogenic temperatures to enhance signal from the scene over instrument background radiation. In order to enable high quality lens designs using silicon and germanium at cryogenic temperatures, we have measured the absolute refractive index of multiple prisms of these two 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 silicon, we report absolute refractive index and thermo-optic coefficient (dn/dT) at temperatures ranging from 20 to 300 K at wavelengths from 1.1 to 5.6 m, while for germanium, we cover temperatures ranging from 20 to 300 K and wavelengths from 1.9 to 5.5 m. 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. Citing the wide variety of values for the refractive indices of these two materials found in the literature, we reiterate the importance of measuring the refractive index of a sample from the same batch of raw material from which final optical components are cut when absolute accuracy greater than ±5 x 10 -3 is desired.

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 NASAs New Frontiers program. This paper discusses the calibration and characterization of LORRI.LORRI consists of a Ritchey-Chrétien 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 × 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.

In order to enable high quality lens designs using calcium fluoride (CaF 2 ) 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 CaF 2 , 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 CaF 2 , 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.

We report on our recent laboratory results with the NASA/Goddard Space Flight Center (GSFC) Visible Nulling Coronagraph (VNC) testbed. We have experimentally achieved focal plane contrasts of 1 x 10 8 and approaching 10 9 at inner working angles of 2 * wavelength/D and 4 * wavelength/D respectively where D is the aperture diameter. The result was obtained using a broadband source with a narrowband spectral filter of width 10 nm centered on 630 nm. To date this is the deepest nulling result with a visible nulling coronagraph yet obtained. Developed also is a Null Control Breadboard (NCB) to assess and quantify MEMS based segmented deformable mirror technology and develop and assess closed-loop null sensing and control algorithm performance from both the pupil and focal planes. We have demonstrated closed-loop control at 27 Hz in the laboratory environment. Efforts are underway to first bring the contrast to > 10 9 necessary for the direct detection and characterization of jovian (Jupiter-like) and then to > 10 10 necessary for terrestrial (Earth-like) exosolar planets. Short term advancements are expected to both broaden the spectral passband from 10 nm to 100 nm and to increase both the long-term stability to > 2 hours and the extent of the null out to a ~ 10 * wavelength / D via the use of MEMS based segmented deformable mirror technology, a coherent fiber bundle, achromatic phase shifters, all in a vacuum chamber at the GSFC VNC facility. Additionally an extreme stability textbook sized compact VNC is under development.

WORD ABSTRACTHerein we report on our contrast assessment and the development, sensing and control of the Vacuum Nuller Testbed to realize a Visible Nulling Coronagraphy (VNC) for exoplanet detection and characterization. The VNC is one of the few approaches that works with filled, segmented and sparse or diluted-aperture telescope systems. It thus spans a range of potential future NASA telescopes and could be flown as a separate instrument on such a future mission. NASA/Goddard Space Flight Center has an established effort to develop VNC technologies, and an incremental sequence of testbeds to advance this approach and its critical technologies. ABSTRACTHerein we report on our contrast assessment and the development, sensing and control of the Vacuum Nuller Testbed to realize a Visible Nulling Coronagraphy (VNC) for exoplanet detection and characterization. Tbe VNC is one of the few approaches that works with filled, segmented and sparse or diluted-aperture telescope systems. It thus spans a range of potential future NASA telescopes and could be flown as a separate instrument on such a future mission. NASA/Goddard Space Flight Center has an established effort to develop VNC technologies, and an incremental sequence of testbeds to advance this approach and its critical technologies. We discuss the development of the vacuum Visible Nulling Coronagraph testbed (VNT). The VNT is an ultra-stable vibration isolated testbed that operates under closed-loop control within a vacuum chamber. It will be used to achieve an incremental sequence of three visible-light nulling milestones with sequentially higher contrasts of 10', 10" and ideally 10 10 at an inner working angle of 2*AID. The VNT is based on a modified Mach-Zehnder nulling interferometer, with a "W" configuration to accommodate a hex-packed MEMS based deformable mirror, a coherent fiber bundle and achromatic phase shifters. We discuss the laboratory results, optical configruation, critical technologies !II1d the null sensing and control approach.