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- J.W. Kooi, J. Kawamura, J. Chen, G. Chattopadhayay,
J. R. Pardo, T.G. Phillips, B. Bumble, J. Stern,
and
H.G. LeDuc.
"A Low Noise NbTiN-based 850 GHz SIS Receiver for the Caltech
Submillimeter Observatory"
Int. J. of Infrared and Mm waves, 21, No. 9 (Sept., 2000).
We have developed a niobium titanium nitride (NbTiN) based
superconductor-insulator-superconductor (SIS) receiver to cover the 350
micron atmospheric window which lies enterely above the energy gap
of niobium (700 GHz), a commonly used superconductor for SIS. The instrument
uses an open structure twin-slot SIS mixer which consists of two Nb/AlN/NbTiN
tunnel junctions, NbTiN thin-film microstrip tuning elements, an a NbTiN
ground plane. The optical configuration is very similar to the 850 GHz
waveguide receiver that was installed at the Caltech Submillimeter
Observatory in 1997. To minimize frot-end loss, we employed reflecting optics
and a cooled beam splitter at 4 K. The instrument has an uncorrected receiver
noise temperature of 205 K DSB at 800 GHz and 410 K DSB at 900 GHz. The
degradation in receiver sensitivity with frequency is primarily due to an
increase in the mixer conversion loss, which is attributed to the mismatch
between the SIS junction and the twin-slot antenna impedance. The overall
system performance has been confirmed through its use at the telescope to
detect a wealth of new spectroscopic lines.
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