17 February 2003 SHARC II: a Caltech submillimeter observatory facility camera with 384 pixels
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Abstract
SHARC II is a background-limited 350 μm and 450 μm facility camera for the Caltech Submillimeter Observatory undergoing commissioning in 2002. The key component of SHARC II is a 12 × 32 array of doped silicon 'pop-up' bolometers developed at NASA/Goddard. Each 1 mm × 1 mm pixel is coated with a 400 Ω/square bismuth film and located λ/4 above a reflective backshort to achieve >75% absorption efficiency. The pixels cover the focal plane with >90% filling factor. At 350 μm, the SHARC II pixels are separated by 0.65 λ/D. In contrast to the silicon bolometers in the predecessor of SHARC II, each doped thermistor occupies nearly the full area of the pixel, which lowers the 1/f knee of the detector noise to <0.03 Hz, under load, at the bath temperature of 0.36 K. The bolometers are AC-biased and read in 'total power' mode to take advantage of the improved stability. Each bolometer is biased through a custom ~130 MΩ CrSi load resistor at 7 K and read with a commercial JFET at 120 K. The JFETs and load resistors are integrated with the detectors into a single assembly to minimize microphonic noise. Electrical connection across the 0.36 K to 4 K and 4 K to 120 K temperature interfaces is accomplished with lithographed metal wires on dielectric substrates. In the best 25% of winter nights on Mauna Kea, SHARC II is expected to have an NEFD at 350 μm of 1 Jy Hz-1/2 or better. The new camera should be at least 4 times faster at detecting known point sources and 30 times faster at mapping large areas compared to the prior instrument.
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Charles Darren Dowell, Christine A. Allen, R. Sachidananda Babu, Minoru M. Freund, Matthew Gardner, Jeff Groseth, Murzy D. Jhabvala, Attila Kovacs, Dariusz C. Lis, Samuel Harvey Moseley, Thomas G. Phillips, Robert F. Silverberg, George M. Voellmer, Hiroshige Yoshida, "SHARC II: a Caltech submillimeter observatory facility camera with 384 pixels", Proc. SPIE 4855, Millimeter and Submillimeter Detectors for Astronomy, (17 February 2003); doi: 10.1117/12.459360; https://doi.org/10.1117/12.459360
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KEYWORDS
Bolometers

Sensors

Field effect transistors

Resistors

Helium

Liquids

Resistance

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