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Doherty, Peter

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Doherty

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Doherty, Peter
Author's Publications: search.filters.isAuthorOfPublication.52e19b63-e096-4d30-b13a-342d6bd98c67

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    Electro-optical testing of fully depleted CCD image sensors for the Large Synoptic Survey Telescope camera
    (Society of Photo-optical Instrumentation Engineers, 2014) Doherty, Peter; Antilogus, Pierre; Astier, Pierre; Chiang, James; Gilmore, D. Kirk; Guyonnet, Augustin; Huang, Dajun; Kelly, Heather; Kotov, Ivan; Kubanek, Petr; Nomerotski, Andrei; O’Connor, Paul; Rasmussen, Andrew; Riot, Vincent J.; Stubbs, Christopher; Takacs, Peter; Tyson, J. Anthony; Vetter, Kurt
    The LSST Camera science sensor array will incorporate 189 large format Charge Coupled Device (CCD) image sensors. Each CCD will include over 16 million pixels and will be divided into 16 equally sized segments and each segment will be read through a separate output amplifier. The science goals of the project require CCD sensors with state of the art performance in many aspects. The broad survey wavelength coverage requires fully depleted, 100 micrometer thick, high resistivity, bulk silicon as the imager substrate. Image quality requirements place strict limits on the image degradation that may be caused by sensor effects: optical, electronic, and mechanical. In this paper we discuss the design of the prototype sensors, the hardware and software that has been used to perform electro-optic testing of the sensors, and a selection of the results of the testing to date. The architectural features that lead to internal electrostatic fields, the various effects on charge collection and transport that are caused by them, including charge diffusion and redistribution, effects on delivered PSF, and potential impacts on delivered science data quality are addressed.
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    Precise Throughput Determination of the PanSTARRS Telescope and the Gigapixel Imager using a Calibrated Silicon Photodiode and a Tunable Laser: Initial Results
    (Institute of Physics, 2010) Stubbs, Christopher; Doherty, Peter; Cramer, Claire; Narayan, Gautham; Brown, Yorke; Lykke, Keith; Woodward, John; Tonry, John
    We have used a precision calibrated photodiode as the fundamental metrology reference in order to determine the relative throughput of the PanSTARRS telescope and the Gigapixel imager, from 400 nm to 1050 nm. Our technique uses a tunable laser as a source of illumination on a transmissive flat-field screen. We determine the full-aperture system throughput as a function of wavelength, including (in a single integral measurement) the mirror reflectivity, the transmission functions of the filters and the corrector optics, and the detector quantum efficiency, by comparing the light seen by each pixel in the CCD array to that measured by a precision-calibrated silicon photodiode. This method allows us to determine the relative throughput of the entire system as a function of wavelength, for each pixel in the instrument, without observations of celestial standards. We present promising initial results from this characterization of the PanSTARRS system, and we use synthetic photometry to assess the photometric perturbations due to throughput variation across the field of view.