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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) [email protected] http://www.mpifr-bonn.mpg.de/staff/gsiringo/polka/polka.html

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Polka a tunable polarimeter for sub mm bolometer arrays l.jpg

PolKaa tunable polarimeter for (sub)mm bolometer arrays

Giorgio Siringo

Bolometer Development

Millimeter & Submillimeter Astronomy Group

Max-Planck-Institut für Radioastronomie (MPIfR)

[email protected]

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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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


Mpifr bolometer arrays l.jpg

  • 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


Mpifr bolometer arrays5 l.jpg

  • 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


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LABOCA-2 Wafer(IPHT, Jena)

288 TES bolometers with integrated SQUIDs

on a 4-inch wafer


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Polarimeter using a half-wave plate (HWP)

  • modulation: a rotating half-wave plate

  • analyzer: a fixed wire-grid polarizer

  • demodulation: a lock-in amplifier


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Polarimeter using a HWP

analyzer horizontal

analyzer vertical

  • The modulation frequency is four times the mechanical one

  • Unpolarized radiation is not modulated (in theory…)


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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


The reflection type hwp rhwp l.jpg

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


The reflection type hwp rhwp11 l.jpg

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


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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 $


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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


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At the telescope


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At the telescope


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At the telescope

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

  • receiver: MPIfR 19 channel [email protected] 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!


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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


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Polarization OO results

an example: 3C279

OO data NOT demodulated

AC coupling

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


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Polarization OO results

Linear polarization was detected on the two quasars

3C279 and 1633+382


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Polarization OO results


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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°


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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)


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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)


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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 l.jpg

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


Ongoing experiments l.jpg

  • 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


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  • 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


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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)

[email protected]

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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