FLASH —
the First Light APEX Submillimeter
Heterodyne instrument
For cooling, a commercial two-stage closed-cycle
FLASH cooler is integrated. To isolate the system (and
make operation at this temperature possible) the
is a dual-channel principal investigator whole system has to be evacuated. In normal ope-
heterodyne instrument operating simulta- ration we maintain a pressure inside the dewar of
neously in the 460 GHz and the 810 GHz 10-6 mbar only. Operation times of several months
atmospheric windows. Design and construc- have been achieved over the last year.
tion of the instrument was launched in late As local-oscillator source we use solid-state
2003; the receiver is in continuous operation chains: a Gunn-oscillator is multiplied several times
now since June 2004. in frequency to reach the desired reference fre-
At present, the highest frequency obser- quency. In our case the multipliers and also the
vation performed at APEX (with FLASH) Gunn-oscillator need to be tuned manually by
was the J=8-7 transition of warm carbon micrometer-screws.
monoxide (CO) at 881 GHz (see the resp.
science flyer). The capability to measure
in two different frequency bands simulta- Use of the system
neously is extremely valuable and current- Over the last year of operation FLASH was
ly unique at APEX. This offers good rela- mainly used to characterize the per-
tive calibration between the two data sets formance of the telescope. The small
which is, e.g., important for excitation stu- beam size of only 7 arc seconds at 810
dies, requiring calibration accuracy. GHz was crucial to properly characte-
rize the telescope at the highest
available frequencies.
Principle of function Two months ago two FFTS (see sepa-
The frequency of the submillimeter radia- rate flyer) as backends where installed.
tion is too high for direct detection and This made possible to launch our science
processing. Therefore, along the hetero- commissioning, requiring wide bandwidth
dyne principle, the high frequency signal coverage with high spectral resolution
is converted first into the frequency range and high reliability.
below 10 GHz, where amplification and As the APEX high-frequency work horse,
processing is possible. FLASH in its present incarnation will stay
For this so-called “mixing” process a in operation until more powerful hetero-
reference source, the “local-oscillator”, dyne detectors like the CHAMP+ array
is needed. The difference signal be- will become available. The receiver will
tween this reference and the sky fre- then be upgraded for use at higher
quency still contains all the spectral in- CAD-model of FLASH frequencies and with new technologies.
formation. As mixing devices we use including the beam-path
so called SIS (superconductor-isola- (green: 460GHz and red:
tor-superconductor) contacts. Working 810GHz). The closed-
near the quantum limit, the mixing de- cycle cooler is shown in
FLASH facts
vice must be operated at 4 K (-269°C). brown. The mixers and
big parts of the optics frequency range [GHz] 420-495 780-887
are inside the vacuum noise performance [K] 200 450
tube. IF bandwidth [GHz] 2-4 4-8
beam (FWHM) [arcsec] 13 7
We acknowledge support from Dr. U.Graf (KOSMA) who made available the design drawings for the FLASH cryostat (which
made possible to manufacture the receiver on shortest possible notice). Dr. G. de Lange (SRON) provided the 800 GHz SIS
mixer. These were invaluable contributions to our successful telescope commissioning.
MPIfR Bonn, 14.07.05
Picture of the APEX-
telescope located at the
Chajnantor high-site in
the Chilenean Andes
Ra
di
at
io
n
Schematics of FLASH:
From the stars to the scientific data … Picture of FLASH installed at
APEX. Visible are the local-
oscillators and the cooling
Telescope and tertiary-
machine (left in the
foreground)
optics
Local Oscilator 1: Local Oscilator 2:
Reference frequency app. Reference frequeny app.
464GHz 812GHz
The LO-control-electronics
Matching optics
Matching optics
Receiver optics
Mixer (460GHz): Mixer (810GHz):
(Reference frequency Observed Signal Polarization Observed Signal (Reference frequency
- (460.5-461.5GHz) (805.5-806.5GHz) -
Observed Frequency) splitter Observed Frequency)
The mixer-control-electronics
2.5-3.5GHz
5.5-6.5GHz
IF-Signal:
IF-Signal:
Backend 1 (FFTS) Spectra of IRC+10216: showing Backend 2 (FFTS)
The IF-processor preparing the (Spectrum analyzer with app.
16.000 independent, rotational transitions of carbon (Spectrum analyzer with app.
16.000 independent,
signal for the spectrometers simultaneous working monoxide (12C0) at ~461 GHz(left simultaneous working
frequency-channels) frequency-channels)
hand side) and ~806 GHz. The line
width is due to the velocity structure
Science
Science
of the source.
data
data
MPIfR Bonn, 14.07.05