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PolKa a tunable polarimeter for (sub)mm bolometer arrays. Giorgio Siringo Bolometer Development Millimeter & Submillimeter Astronomy Group Max-Planck-Institut für Radioastronomie (MPIfR) gsiringo@mpifr-bonn.mpg.de http://www.mpifr-bonn.mpg.de/staff/gsiringo/polka/polka.html

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PolKaa tunable polarimeter for (sub)mm bolometer arrays

Giorgio Siringo

Bolometer Development

Millimeter & Submillimeter Astronomy Group

Max-Planck-Institut für Radioastronomie (MPIfR)

gsiringo@mpifr-bonn.mpg.de

http://www.mpifr-bonn.mpg.de/staff/gsiringo/polka/polka.html

BPol Workshop - October 25-27, 2006

PolKa = Polarimeter für Bolometer Kameras


PolKaa tunable polarimeter for (sub)mm bolometer arrays

PolKa team

Giorgio Siringo

Ernst Kreysa

Lothar A. Reichertz

Collaboration

Giuseppe Cimò

Thomas Krichbaum

IPHT, Jena

Bolometer Development

Group @ MPIfR

Walter Esch

Hans-Peter Gemünd

Ernst Kreysa (group leader)

Gundula Lundershausen

Giorgio Siringo

PolKa = Polarimeter für Bolometer Kameras


  • HUMBA: Hundred Millikelvin Bolometer Array (discontinued)

    • 19 NTD bolos, DC biased, AC coupled,

    • l = 2 mm (150 GHz), 100 mK (dilution fridge)

    • Used at the HHT and IRAM 30 m to observe SZ effect

  • HHT 19-channel Array: (discontinued)

    • 19 NTD bolos, DC biased, AC coupled

    • l = 850 mm (350 GHz) , 300 mK

    • Facility instrument at the Heinrich Hertz Telescope (HHT)

  • SIMBA: SEST Imaging Bolometer Array(discontinued)

    • 37 NTD bolos, DC biased, AC coupled + 5 AC biased and DC coupled

    • l = 1.2 mm (250 GHz) , 300 mK

    • Used in fast scanning without chopping secondary

    • Facility instrument at the Swedish-ESO Submillimeter Telescope (SEST)

MPIfR Bolometer Arrays


  • MAMBO (Max-Planck Millimeter Bolometer)

    • NTD bolos, DC biased, AC coupled, l = 1.2 mm (250 GHz) , 300 mK

    • MAMBO-1: 37 elements

    • MAMBO-2: 117 elements

    • Facility instruments on the IRAM 30 m telescope, Pico Veleta, Spain

  • LABOCA (Large APEX Bolometer Camera)

    • 295 NTD bolos, AC biased, DC coupled, l = 850 mm (350 GHz) , 300 mK

    • Facility instrument on the APEX telescope (Atacama Pathfinder Experiment, Llano de Chajnantor, Chile)

  • SABOCA (Submillimeter APEX Bolometer Camera)

    • 37 TES bolos + SQUIDs multiplexing and amplification

    • = 350 mm (860 GHz) , 300 mK

      To be installed as facility instrument on the APEX telescope in early 2007

  • LABOCA-2 (Large APEX Bolometer Camera)

    • 288 TES bolos + SQUIDs multiplexing and amplification

    • Will replace LABOCA at the end of 2007

    • TES development in collaboration with IPHT (Institute for Physical High Technology) of Jena

MPIfR Bolometer Arrays


LABOCA-2 Wafer(IPHT, Jena)

288 TES bolometers with integrated SQUIDs

on a 4-inch wafer


Polarimeter using a half-wave plate (HWP)

  • modulation: a rotating half-wave plate

  • analyzer: a fixed wire-grid polarizer

  • demodulation: a lock-in amplifier


Polarimeter using a HWP

analyzer horizontal

analyzer vertical

  • The modulation frequency is four times the mechanical one

  • Unpolarized radiation is not modulated (in theory…)


The PolKa polarimeter

  • PolKa is designed to be used with any of the MPIfR bolometer arrays (large diameter, wide range of wavelengths)

  • It uses a reflection-type HWP to modulate the polarization (crystal-type have stronger absorption and it is difficult to produce large diameters)

  • The HWP isrotated continuously by a precision motorized air-bearing: no chopping secondary mirror

  • Raw data (not demodulated) are acquired (fast data acquisition)

  • Demodulation made offline via a “software lock-in” algorithm


polarizer

mirror

The reflection-type HWP (RHWP)

The RHWP is made of two parts:

  • a wire-grid polarizer

  • a flat metallic mirror

    By tuning the distance t between the two parts it is possible to produce a 180° phase shift between the two components of polarization for any operating wavelength

    This device uses metallic reflections and absorption is negligible


polarizer

mirror

The reflection-type HWP (RHWP)

but:

  • large wire-grid polarizers are needed

  • they are produced only in a few labs in the world

  • have very long delivery time (order of years)

  • are expensive (in the range 103 - 105 $)

We decided to produce them in our labs


Wire-grid production

  • ~4000 tungsten wires

  • wire size: 20 mm

  • step: 63 mm

  • position error:

    ~ 15 mm rms

  • clear aperture: 246 mm

  • market price:

    ~ 10,000 $


At the telescope

Heinrich Hertz submillimeter

Telescope (HHT),

Mount Graham,

~120 Km north-east of

Tucson, Arizona

3,186 m above the see level

diameter: 10 m

surface accuracy: 15 mm rms


At the telescope


At the telescope


At the telescope

  • the 246 mm version of PolKa was tested at the HHT on Jan 2002

  • receiver: MPIfR 19 channel array@850 mm

  • rotation frequency: 3.5 Hz

  • polarization modulation: 14 Hz

  • full size HWP: full 19 channel array on the sky

  • improved analyzer system

    and... we had excellent weather!


At the telescope

Observing modes

We had two main observational strategies:

  • Polarization On-Off: to perform polarized flux measurements or detection experiments. Used on point sources.

    NEFD ~ 1650 mJy t(1/2) /(20” beam)

  • Polarization On-the-Fly maps: to map the polarization pattern of extended sources.

    NEFD ~ 380 mJy/(20” beam) per coverage (6’x6’, t~0.5 h)

    complemented by

  • Total power measurements: to get I and for point, focus, skydip


Polarization OO results

an example: 3C279

OO data NOT demodulated

AC coupling

The signal is strong enough to be fitted using a sine!


Polarization OO results

Linear polarization was detected on the two quasars

3C279 and 1633+382


Polarization OO results


Ori OMC-1

Coppin & al., A&A 356 (2000)

Polarization OtF results

A comparison: SCUBA-Pol

  • SCUBA-Pol @ JCMT:

    • 4092 m above the see level

    • 15 m telescope

    • 850 mm

    • Crystal type HWP

    • Step & integrate + wobbler

  • PolKa @ HHT:

    • 3186 m above the see level

    • 10 m telescope

    • 850 mm

    • Reflection type HWP

    • Continuous spinning & no wobbler

SCUBA-Pol map

Length = pol. degree

Vectors rotated by 90°


Length = pol. degree

Vectors rotated by 90°

12 maps co-added:

~ 6 h

pol. degree map

Coppin & al., A&A 356 (2000)

Siringo & al., A&A 422 (2004)


SCUBA-Pol / ~7 h int.time

Orion OMC-3 MMS3-4

PolKa map / 1.5 h int. time (3 scans)

pol.intensity map

B.C.Matthews & al., ApJ, 562 (2001)


Contours = CO(6-5)

Grey-scale = 1.2 mm continuum

IRAS 05358+3543

H.Beuther & al., A&A, 387 (2002)

pol. degree map

~ 3 h int. time (6 scans)


Summary

  • We proposed a new concept of polarimeter for mm/submm wavelengths: RHWP + continuous spinning - wobbler

  • Results:

    • polarization detection on 3C279 and 1633+382

    • polarization variability of 3C279

    • high resolution polarization maps of Orion OMC-1, MMS3/4 in Orion OMC-3, IRAS 05358+3543

  • The good points of PolKa are:

    • tunable over a wide range of wavelengths

    • low insertion loss (RHWP)

    • easy changeover between polarimetry and photometry

    • high modulation efficiency

    • high imaging quality (no chopping mirror)

  • These results confirm that the new concept is valid


  • We have 2 new RHWP units for our active experiments:

  • MAMBO-1 on the IRAM 30m telescope

    • Pico Veleta, Spain (3000 m amsl)

    • larger telescope: 30 m dish

    • longer wavelength: receiver MAMBO-1@ 1.2 mm

    • more sensitivity: MAMBO-1 has 37 bolometers

    • higher resolution: 11” beam

  • LABOCA on APEX

    • better site: Llano de Chajnantor, Chile (5,100 m amsl)

    • submillimeter telescope: 12 m dish, 15 mm rms

    • wavelength: 850mm

    • large array: 295 bolometers

    • high resolution: 18” beam

    • larger array: 11’

    • fast mapping speed: 2’/s

    • higher sensitivity: 1 square degree in 1.5 hour, 125 mJy rms noise level

Ongoing experiments


  • Contributions to BPol from ground based polarimeters:

  • Foreground observations (dust)

  • Instrument calibrations

  • Complications:

  • Small angular scale

  • Limitations due to the atmosphere

  • Available ground based polarimeters with bolometers:

  • QUaD, South Pole (optimized for CMB), 100-150 GHz

  • PolKa + MAMBO-1, Pico Veleta, Spain, 250 GHz

  • PolKa + LABOCA, APEX, Chile, 350 GHz

  • SHARP + SHARC-II, CSO, Hawaii, 860 GHz

Hints for discussion


PolKaa tunable polarimeter for (sub)mm bolometer arrays

Giorgio Siringo

Bolometer Development

Millimeter & Submillimeter Astronomy Group

Max-Planck-Institut für Radioastronomie (MPIfR)

gsiringo@mpifr-bonn.mpg.de

http://www.mpifr-bonn.mpg.de/staff/gsiringo/polka/polka.html

BPol Workshop - October 25-27, 2006

PolKa = Polarimeter für Bolometer Kameras


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