LABOCA
Large APEX Bolometer Camera
Giorgio Siringo
Bolometer Development
Millimeter & Submillimeter Astronomy Group
Direct...
LABOCA
Large APEX Bolometer Camera
Bolometer
Development
Group @ MPIfR
Walter Esch
Hans-Peter Gemünd
Ernst Kreysa (group l...
LABOCA
Large APEX Bolometer Camera

Introduction
LABOCA key facts – 1: the instrument
Bolometric continuum receiver
for operation in the 870 µm atmospheric window (345 GHz...
LABOCA key facts – 2: on APEX
Commissioned in May 2007 as facility instrument
on the APEX telescope
•High-efficiency teles...
LABOCA timeline
•2003: initial design
•2004: development (first wafers, design of the electronics, …)
•2005: extensive tes...
LABOCA
Large APEX Bolometer Camera

Technical Overview
Tertiary Optics
•Installed in the Cassegrain
cabin of APEX
•Receiver and M4-M7 mounted
on hexapod positioners
M6

LABOCA

...
Tertiary Optics
M2

M1

f/8 at APEX
focal plane

side view

M3

The task of the optics is to transform the f-ratio from f/...
Tertiary Optics

M5
M7
M2
M4

lens
M1

f/1.75 at
LABOCA
focal plane

M6

view from above

f/8 at APEX
focal plane

M3

M6
...
Tertiary Optics

spot diagram with Airy disk for λ = 350 µm
Strehl ratio > .995

.1442 deg
max distortion:10%

The task is...
Bolometer Array
295 semiconducting composite bolometer for
operation at 300 mK and 870 µm wavelength (345 GHz)

An absorbe...
Bolometer Array
295 semiconducting composite bolometer for
operation at 300 mK and 870 µm wavelength (345 GHz)
870 µm

NTD...
Bolometer Array
A naked array:
•wiring side
•4” Si wafer
•295 bolometers

Manufactured by
E. Kreysa at the
Berkeley Microl...
Bolometer Array
A naked array:
•wiring side
•4” Si wafer
•295 bolometers

1 central beam
9 concentric hexagons
+other 6x5 ...
Bolometer Array
Pictures of the two sides of the array

NTDs are attached on the wiring side
(only manual step in the manu...
Bolometer Array

wiring side
bonding wires
(backreflector at λ/4)

other side: array of conical horn antennas
RF filters
b...
Bolometer Array

295 conical horns machined
in a single aluminum block
(manufactured at MPIfR)
Bolometer Array

cut

cut

Si wafer

backreflector

front

NTD

niobium
wires
Cryogenics

•At APEX (5107 m above the sea level) the air pressure
(~540 mbar) is almost half of the standard one:
•liquid...
Cold Optics

band-pass filter
at helium shield

low-pass filter
at nitrogen shield

•Filters designed and assembled at MPI...
Cold Optics

LABOCA – The Large APEX Bolometer Camera

G. Siringo, MPIfR
Cold Electronics

(30 MOhm nichrome/Si, MSI)

focal plane

sorption cooler
sorption cooler

312 channels:
12 printed circu...
Cold Electronics

12 boards
26 bias resistors
per board

sorption cooler
sorption cooler

array

liquid
helium
tank

12 fl...
Cold Electronics

•3 structured printed circuit boards per box

sorption cooler
sorption cooler

• 312 JFET impedence adap...
Data Readout

top view

Outside the cryostat
320 channels:
295 bolometers
+
25 extra lines
side view

320 amplifiers in 4 ...
Data Readout
4 data acquisition (DAQ) boards
in the backend computer
80 channels per board, in a
modular 1-to-1 scheme:
1 ...
Data Readout
•The data acquisition hardware provides a reference frequency for the AC biasing:
the AC bias is thus synchro...
Data Readout
•AC biasing, DC coupling: low 1/f onset, clean post-detection bandwidth down to 0.1 Hz

1/f

noise floor

~ 0...
Data Reduction
•A new software package has been specifically developed to reduce LABOCA
data: the Bolometer array data Ana...
LABOCA
Large APEX Bolometer Camera

LABOCA on Sky
LABOCA On Sky
Performance
• 248/295 useful channels (84%)
•2 blinded to monitor temperature and noise
•18 show high noise
...
LABOCA On Sky
Performance
•The beam shape was derived for individual
bolometers from
•beam-maps on Mars
•pointing scans on...
LABOCA On Sky
Performance
• Mean point-source sensitivity of the array: 53 mJy·sqrt(s)
(NEFD per channel, low frequencies ...
LABOCA On Sky
Observing Modes
•The frequencies of the signal produced by scanning across the source
must fall into the whi...
LABOCA On Sky
Observing Modes
Mapping modes
•On-the-fly maps (otf): rectangular scanning patterns with a constant scanning...
LABOCA On Sky
Observing Modes
Example of a raster of spirals:
spiral mapping mode
combined with a raster
map of 25 positio...
LABOCA On Sky
Calibrations
•Calibration accuracy, based on planets: ~5-10%
(depending on weather stability)

• Sky opacity...
LABOCA On Sky
ATLASGAL: APEX Telescope Large Area Survey of the Galaxy
MPIfR Bonn (Schuller et al., in prep.) + MPIA Heide...
LABOCA On Sky

NGC 253

Nearby Galaxies
Cen A

NGC 4945

First detection at 870 µm
NGC 253: 8 h - rms: 3.5 mJy/b
Cen A:
5 ...
LABOCA On Sky
Chandra Deep Field – South (CDFS)

30’ x 30’ deep field
200 hour of integration
rms: 1.5 mJy/beam

63 source...
LABOCA
Large APEX Bolometer Camera
The future
In collaboration with the Institute for Photonics Technology (IPHT)
of Jena ...
350 µm map of the NGC6334 molecular cloud – SABOCA on APEX - May 16, 2008
total observing time: 1h 40m, including observat...
Talk g siringo_laboca_spie20080626_last
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G. Siringo
talk about LABOCA,
SPIE conference, Marseille June 2008.

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Talk g siringo_laboca_spie20080626_last

  1. 1. LABOCA Large APEX Bolometer Camera Giorgio Siringo Bolometer Development Millimeter & Submillimeter Astronomy Group Director: Karl M. Menten Max-Planck-Institut für Radioastronomie (MPIfR) gsiringo@mpifr-bonn.mpg.de http://www.mpifr-bonn.mpg.de/staff/gsiringo SPIE 2008 - June 26, 2008
  2. 2. LABOCA Large APEX Bolometer Camera Bolometer Development Group @ MPIfR Walter Esch Hans-Peter Gemünd Ernst Kreysa (group leader) Gundula Lundershausen Giorgio Siringo Students Nikhil Jethava (now at NIST) Angel Colin (now Uni-Cantabria) LABOCA commissioning team Giorgio Siringo Ernst Kreysa Axel Weiß Attila Kovacs Frederic Schuller Collaboration E.Haller & J.Beeman (LBNL Berkeley) Frank Bertoldi (Uni-Bonn) Alexandre Beelen (Uni-Bonn) Lars-Åke Nyman (ESO)
  3. 3. LABOCA Large APEX Bolometer Camera Introduction
  4. 4. LABOCA key facts – 1: the instrument Bolometric continuum receiver for operation in the 870 µm atmospheric window (345 GHz) •Large array: 295 semiconducting composite bolometers •Antenna-coupled •DC-coupling: total power receiver •AC-bias + real-time DSP: large, clean, post-detection frequency band •Designed and assembled by the bolometer group of MPIfR, Bonn LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  5. 5. LABOCA key facts – 2: on APEX Commissioned in May 2007 as facility instrument on the APEX telescope •High-efficiency telescope: 12 m submillimeter telescope with 15 µm surface accuracy (~ λ/50) •On Llano de Chajnantor: 5100 m, extremely good atmospheric conditions for most of the year •Large field of view: diameter = 11’.4 and high resolution: 1 beam = 19” FWHM •Operated without chopping secondary mirror, therefore •No limitations on the scan pattern •Continuous scanning mode, scanning speed up to 4’/s Largest/fastest camera for mapping sub-mm continuum LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  6. 6. LABOCA timeline •2003: initial design •2004: development (first wafers, design of the electronics, …) •2005: extensive testing on a pulse-tube cooling machine, but Test failed! High noise induced by the pulses Moved to a different design based on a wet cryostat •September 2006: installation on APEX and first light •May 2007: successfully commissioned •Since June 2007 - today: routinely operated as facility instrument •First year of operation: •two observing semesters •about 2000 hours of observations •more than 6000 hours requested LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  7. 7. LABOCA Large APEX Bolometer Camera Technical Overview
  8. 8. Tertiary Optics •Installed in the Cassegrain cabin of APEX •Receiver and M4-M7 mounted on hexapod positioners M6 LABOCA M7 M5 M3 LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  9. 9. Tertiary Optics M2 M1 f/8 at APEX focal plane side view M3 The task of the optics is to transform the f-ratio from f/8 at the Cassegrain focus to f/1.75 at the horn array, while correcting the aberrations over the whole field (~12’) under the constraint of having parallel output beams The final design is diffraction limited even for 350 µm wavelength LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  10. 10. Tertiary Optics M5 M7 M2 M4 lens M1 f/1.75 at LABOCA focal plane M6 view from above f/8 at APEX focal plane M3 M6 side view M3 side view M5 M7 M3 LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  11. 11. Tertiary Optics spot diagram with Airy disk for λ = 350 µm Strehl ratio > .995 .1442 deg max distortion:10% The task is to transform the f-ratio from f/8 at the Cassegrain focus to f/1.75 at the horn array, while correcting the aberrations over the whole field (.2 deg) under the constraint of having parallel output beams The final design is diffraction limited even for 350 µm wavelength LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  12. 12. Bolometer Array 295 semiconducting composite bolometer for operation at 300 mK and 870 µm wavelength (345 GHz) An absorber is kept at low temperature by a weak thermal link to a heat sink Photons Absorption of photons produces a temporary increase in the temperature of the absorber A ultra-sensitive thermometer (thermistor) transforms the temperature variations of the absorber in electric signals The electric signals are consequently amplified and processed by electronic devices LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  13. 13. Bolometer Array 295 semiconducting composite bolometer for operation at 300 mK and 870 µm wavelength (345 GHz) 870 µm NTD-Ge Thermal+mechanical support: unstructured silicon nitride membrane (400 nm) Absorber: titanium layer Thermistor: neutron-transmutation doped (NTD) germanium semiconducting chips (from E. E. Haller and J. W. Beeman) Electrical connection: gold and niobium wires LABOCA – The Large APEX Bolometer Camera Photons Ti layer 0.4 µm Si3N4 membrane 300 mK G. Siringo, MPIfR
  14. 14. Bolometer Array A naked array: •wiring side •4” Si wafer •295 bolometers Manufactured by E. Kreysa at the Berkeley Microlab LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  15. 15. Bolometer Array A naked array: •wiring side •4” Si wafer •295 bolometers 1 central beam 9 concentric hexagons +other 6x5 bolometers LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  16. 16. Bolometer Array Pictures of the two sides of the array NTDs are attached on the wiring side (only manual step in the manufacture) LABOCA – The Large APEX Bolometer Camera opposite side: bolometer cells G. Siringo, MPIfR
  17. 17. Bolometer Array wiring side bonding wires (backreflector at λ/4) other side: array of conical horn antennas RF filters bias circuitry load resistors LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  18. 18. Bolometer Array 295 conical horns machined in a single aluminum block (manufactured at MPIfR)
  19. 19. Bolometer Array cut cut Si wafer backreflector front NTD niobium wires
  20. 20. Cryogenics •At APEX (5107 m above the sea level) the air pressure (~540 mbar) is almost half of the standard one: •liquid nitrogen provides thermal shielding at ~73 K •liquid helium provides thermal shielding at ~3.7 K •The cryostat must be refilled once per day sorption cooler sorption cooler •The cryostat of LABOCA incorporates •a 3-liter reservoir of liquid nitrogen •a 5-liter reservoir of liquid helium liquid helium tank •The operation temperature of 290 mK is provided by a two-stage closed-cycle sorption cooler •The system works without pumping on the helium bath liquid nitrogen tank LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  21. 21. Cold Optics band-pass filter at helium shield low-pass filter at nitrogen shield •Filters designed and assembled at MPIfR •Theoretical support and electromagnetic simulations by V. Hansen (University of Wuppertal, Germany) •Band-pass formed by an interference filter made of inductive and capacitive meshes embedded in polypropylene •The low frequency edge of the band is defined by the cut-off of the cylindrical waveguide embedded in the horn antennas. •A freestanding inductive mesh behind the window provides shielding against radio frequency interference LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  22. 22. Cold Optics LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  23. 23. Cold Electronics (30 MOhm nichrome/Si, MSI) focal plane sorption cooler sorption cooler 312 channels: 12 printed circuit boards 26 bias resistors each liquid helium tank RF filters LABOCA – The Large APEX Bolometer Camera liquid nitrogen tank G. Siringo, MPIfR
  24. 24. Cold Electronics 12 boards 26 bias resistors per board sorption cooler sorption cooler array liquid helium tank 12 flat cables 1 cable = 26 manganin wires embedded in Kapton liquid helium cold plate LABOCA – The Large APEX Bolometer Camera liquid nitrogen tank G. Siringo, MPIfR
  25. 25. Cold Electronics •3 structured printed circuit boards per box sorption cooler sorption cooler • 312 JFET impedence adapters in 4 boxes thermally shunted to the liquid nitrogen bath •26 JFET per board self heated to ~120 K liquid helium tank liquid nitrogen tank LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  26. 26. Data Readout top view Outside the cryostat 320 channels: 295 bolometers + 25 extra lines side view 320 amplifiers in 4 identical units: •16 printed circuit boards per unit •5 low-noise, high-gain amplifiers per board for a total of 80 channels per unit The amplification units also provide the AC bias circuitry and perform real-time demodulation LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  27. 27. Data Readout 4 data acquisition (DAQ) boards in the backend computer 80 channels per board, in a modular 1-to-1 scheme: 1 DAQ board = 1 amplif. unit backend computer 4x(20x4) via a direct (private) network, the data are sent to the bridge computer LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  28. 28. Data Readout •The data acquisition hardware provides a reference frequency for the AC biasing: the AC bias is thus synchronized to the data sampling •AC biasing: low 1/f onset, clean post-detection bandwidth down to 0.1 Hz  crucial for the detection of large structures in fast mapping mode •Use of a bridge computer: data sampled at high rate (1 kHz) by the DAQ hardware are low-pass filtered and downsampled in real-time •Data stored in MB-FITS format (Multi-Beam FITS) by the data writer embedded in the APEX Control Software (APECS) •Use of a frontend computer: allows remote monitor and control of the electronics (gain setting, DC offset removal) and of part of the cryogenics (temperature monitor, operation of the sorption cooler, automatic recycling) LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  29. 29. Data Readout •AC biasing, DC coupling: low 1/f onset, clean post-detection bandwidth down to 0.1 Hz 1/f noise floor ~ 0.1 Hz LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  30. 30. Data Reduction •A new software package has been specifically developed to reduce LABOCA data: the Bolometer array data Analysis software (BoA) •Mostly written in Python, except for the most demanding tasks, written in Fortran90 •BoA was first installed and integrated in APECS in early 2006 (extensive description in Schuller et al. in prep.) •The BoA software can be used to process any kind of bolometer data acquired at APEX •During the observations, the online-BoA (as part of APECS) performs a quick data reduction of each scan, to provide the observer with a quick preview of the maps being observed. In particular, for the basic pointing and focus scans, it computes and sends back to the observer the pointing offsets or focus corrections to be applied LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  31. 31. LABOCA Large APEX Bolometer Camera LABOCA on Sky
  32. 32. LABOCA On Sky Performance • 248/295 useful channels (84%) •2 blinded to monitor temperature and noise •18 show high noise •29 dead Footprint of LABOCA on sky from a beam-map on Mars •Positions and relative gains of each bolometer are derived from fully sampled maps (beam-maps) on the planets Mars and Saturn The circles represent the FWHM shape of the 248 beams on sky by 2-dimensional Gaussian fit to the single-channel map of each bolometer Only bolometers with useful signalto-noise are shown in this map. LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  33. 33. LABOCA On Sky Performance •The beam shape was derived for individual bolometers from •beam-maps on Mars •pointing scans on Uranus and Neptune Both methods lead to comparable results •The main beam is well described by a Gaussian with a FWHM of 19”.2 ± 0”.7 •The beam starts to deviate at ~ -20 dB Radial profile of the LABOCA beam derived averaging the beams of all functional bolometers (248) from fully sampled maps on Mars The error bars show the standard deviation LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  34. 34. LABOCA On Sky Performance • Mean point-source sensitivity of the array: 53 mJy·sqrt(s) (NEFD per channel, low frequencies filtering applied) • Extended emission sensitivity: 95 mJy · sqrt(s) (without low frequencies filtering) Number of bolometers per sensitivity interval LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  35. 35. LABOCA On Sky Observing Modes •The frequencies of the signal produced by scanning across the source must fall into the white noise part of the post-detection frequency band (0.1 - 20 Hz) •Min scanning speed: 30"/s minimum required for sufficient source modulation, depends on the atmospheric stability and source shape •Max scanning speed: 4'/s limited by the time resolution in the coordinates given by the telescope’s control software •Possible scan patterns limited by the telescope’s control software, which allows only constant speed, in rectangular or polar coordinates: spiral patterns are possible LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  36. 36. LABOCA On Sky Observing Modes Mapping modes •On-the-fly maps (otf): rectangular scanning patterns with a constant scanning linear speed, in horizontal or equatorial coordinates. For maps on the scale of the FoV up to a few degrees •Spirals: done with a constant angular speed in polar coordinates, the linear scanning velocity is not constant. In ~30 s can produce a fully sampled map for the FoV with linear scanning velocities limited between 1’/s and 4’/s •Rasters of spirals: for fainter sources, the basic spiral pattern can be combined with a raster grid of pointing positions resulting in an denser sampling and longer integration time. This mode gives excellent results for sources smaller than the FoV and is suitable for integrations on faint sources Other modes •Pointing: short spiral, offsets determined with a 2-dimensional Gaussian fit •Focus: 5 s integration on a bright source at 5 different subreflector positions •Skydip: a continuous tip scan in elevation, to measure the power of the atmospheric emission as function of the airmass LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  37. 37. LABOCA On Sky Observing Modes Example of a raster of spirals: spiral mapping mode combined with a raster map of 25 positions pattern in Az/El of the central beam of the array complete scan = 12 minutes final map = 2000x2000 arcsec with uniform rms residual noise LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  38. 38. LABOCA On Sky Calibrations •Calibration accuracy, based on planets: ~5-10% (depending on weather stability) • Sky opacity is determined with skydips •Secondary calibrators list available (based on MAMBO and SCUBA lists) Example of calibration on planets: 5 observing runs on consecutive days LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  39. 39. LABOCA On Sky ATLASGAL: APEX Telescope Large Area Survey of the Galaxy MPIfR Bonn (Schuller et al., in prep.) + MPIA Heidelberg + ESO + Uni. de Chile Unbiased survey of the inner Galactic Plane at 870 µm Goal: mapping |l| ≤ 60°, |b| ≤ 1.5°, down to 50 mJy/beam 2007: covered 95 deg2 in ~75 hours of observing time 2008: covered another 150 deg2 , project ongoing… 4x2 deg2 map of the Galactic Center (courtesy of F. Schuller) Integration time: 6 hours only - rms: 50 mJy/beam FoV LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  40. 40. LABOCA On Sky NGC 253 Nearby Galaxies Cen A NGC 4945 First detection at 870 µm NGC 253: 8 h - rms: 3.5 mJy/b Cen A: 5 h - rms: 4.0 mJy/b NGC 4945: 3 h - rms: 5.0 mJy/b (courtesy of A. Weiß, submitted to A&A) LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  41. 41. LABOCA On Sky Chandra Deep Field – South (CDFS) 30’ x 30’ deep field 200 hour of integration rms: 1.5 mJy/beam 63 sources detected S/N pixel histogram (1 pixel=1/3 of beam) rms vs time Weiss, Smail, Walter et al. LABOCA – The Large APEX Bolometer Camera G. Siringo, MPIfR
  42. 42. LABOCA Large APEX Bolometer Camera The future In collaboration with the Institute for Photonics Technology (IPHT) of Jena we are already working on LABOCA-2 : a new bolometer array using superconducting technology • TES (transition edge sensor) thermistors • dipole absorbers • SQUID multiplexing and amplification A system already using the same technology, SABOCA the Submillimeter APEX Bolometer Camera (870 GHz) has been succesfully tested on APEX last May and will be commissioned in October 2008 as facility instrument (see also N. Jethava’s talk about TES in the afternoon) Given the low sensitivity of superconducting bolometers to microphonics, it will be possible to move from the wet cryostat to a pulse-tube cooler: already succesfully tested in our labs in Bonn
  43. 43. 350 µm map of the NGC6334 molecular cloud – SABOCA on APEX - May 16, 2008 total observing time: 1h 40m, including observations of calibrators; units: Jy/beam SABOCA = Submillimeter APEX Bolometer Camera (350 µm) 37-elements TES + SQUIDs multiplexing and amplification LABOCA map

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