A new state-of-the-art balloon borne three channel (500GHz,
625GHz, 1.8 THz) cryogenic heterodyne spectrometer will allow
enhanced limb sounding of the Earth's atmosphere within the
submillimeter and far-infrared spectral range. The instrument,
called TELIS (TErahertz and submm LImb Sounder), is being
developed by a consortium of major European institutes that
includes the Space Research Organisation of the Netherlands
(SRON), the Rutherford Appleton Laboratory (RAL) in the United
Kingdom and the Deutschen Zentrum für Luft- und Raumfahrt (DLR) in
Germany (lead institute). TELIS will utilise state-of-the-art
superconducting heterodyne technology and is designed to be
compact and lightweight, while providing broad spectral coverage,
high spectral resolution and long flight duration. Target species
are key atmospheric short-lived radicals such as OH, HO2, ClO,
BrO together with stable constituents such as O3, HCl and HOCl.
TELIS will consist of a common front end with a cassegrain based
pointing telescope, common transfer optics and a digital
autocorrelator spectrometer for each channel.
One of the three receiver channels (developed by DLR) will focus
on the measurement of the OH-triplett at 1.8 THz. Low noise NbN
based Hot Electron Bolometers will be acting as heterodyne mixing
elements. A Martin Puplett Interferometer designed for cryogenic
operation in the cryostat is used to interfer signal- and LO
radiation generated by a solid state based local oscillator unit.
Recently athe laboratory DSB version of the TELIS heterodyne receiver
(using a far infrad laser as preliminary LO source) has been set
up and tested successfully. In this paper the current status of
the THz-channel design and development in the framework of the
TELIS project will be presented