PolKaa tunable polarimeter for (sub)mm

bolometer arrays

Giorgio SiringoBolometer Development

Millimeter & Submillimeter Astronomy GroupMax-Planck-Institut für Radioastronomie (MPIfR)

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

BPol Workshop - October 25-27, 2006

PolKa = Polarimeter für Bolometer Kameras

Bolometer Development Group @ MPIfR

Walter EschHans-Peter GemündErnst Kreysa (group leader)Gundula LundershausenGiorgio Siringo

PolKa team

Giorgio SiringoErnst KreysaLothar A. Reichertz

Collaboration

Giuseppe CimòThomas KrichbaumIPHT, Jena

PolKaa tunable polarimeter for (sub)mm

bolometer arrays

PolKa = Polarimeter für Bolometer Kameras

MPIfR Bolometer Arrays

• HUMBA: Hundred Millikelvin Bolometer Array (discontinued)

19 NTD bolos, DC biased, AC coupled, = 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 = 850 m (350 GHz) , 300 mKFacility 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 = 1.2 mm (250 GHz) , 300 mKUsed in fast scanning without chopping secondaryFacility instrument at the Swedish-ESO Submillimeter Telescope (SEST)

MPIfR Bolometer Arrays

• MAMBO (Max-Planck Millimeter Bolometer)NTD bolos, DC biased, AC coupled, = 1.2 mm (250 GHz) , 300 mK MAMBO-1: 37 elements MAMBO-2: 117 elementsFacility instruments on the IRAM 30 m telescope, Pico Veleta, Spain

• LABOCA (Large APEX Bolometer Camera)295 NTD bolos, AC biased, DC coupled, = 850 m (350 GHz) , 300 mKFacility 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 m (860 GHz) , 300 mKTo be installed as facility instrument on the APEX telescope in early 2007

• LABOCA-2 (Large APEX Bolometer Camera)288 TES bolos + SQUIDs multiplexing and amplificationWill replace LABOCA at the end of 2007

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

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

z

incoming radiation

rotating HWP(modulator)

fixed polarizer(analyzer)

bolometer

lock-inamplifier

Stokesparameters

(demodulator)

reference signal

• The modulation frequency is four times the mechanical one

• Unpolarized radiation is not modulated (in theory…)

Polarimeter using a HWP

tUtQItI sin44cos2

1 tUtQItI sin44cos

2

1

analyzer horizontal analyzer vertical

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 is rotated 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)

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

mirror

polarizer

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

mirror

polarizer

The reflection-type HWP (RHWP)

• ~4000 tungsten wires

• wire size: 20 m

• step: 63 m

• position error:

~ 15 m rms

• clear aperture: 246 mm

• market price:

~ 10,000 $

Wire-grid production

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 m 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 m

• 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

At the telescope

Polarization OO resultsan example: 3C279

0 45 90 135 180 225 270 315 360

-4

-3

-2

-1

0

1

2

3

4

5 xc 11.87753 ±1.19409w 44.97461 ±0.28471A 1.60971 ±0.075

ch 1- 1254 - V

coun

ts

rotation angle [deg]

0 45 90 135 180 225 270 315 360-5

-4

-3

-2

-1

0

1

2

3

4

5

coun

ts

rotation angle [deg]

ch 1- 1253 - Hxc -36.47097 ±0.76713w 45.47148 ±0.15133A 1.79305 ±0.04353

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

OO data NOT demodulated

AC coupling

tUtQItI sin44cos2

1 tUtQItI sin44cos

2

1

Linear polarization was detected on the two quasars3C279 and 1633+382

Polarization OO results

Polarization OO results

• PolKa @ HHT:– 3186 m above the see level– 10 m telescope

– 850 m– Reflection type HWP– Continuous spinning & no wobbler

A comparison: SCUBA-Pol

• SCUBA-Pol @ JCMT:– 4092 m above the see level– 15 m telescope

– 850 m– Crystal type HWP– Step & integrate + wobbler

SCUBA-Pol mapLength = pol. degreeVectors rotated by 90°

Ori OMC-1

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

Polarization OtF results

pol. degree map

Length = pol. degreeVectors rotated by 90°

12 maps co-added: ~ 6 h

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

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

Orion OMC-3 MMS3-4PolKa map / 1.5 h int. time (3 scans)

SCUBA-Pol / ~7 h int.time

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

pol.intensity map

Contours = CO(6-5)Grey-scale = 1.2 mm continuum

IRAS 05358+3543

~ 3 h int. time (6 scans)

pol. degree map

H.B

eu

ther &

al., A

&A

, 38

7 (2

00

2)

Summary

• 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)

• 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

• These results confirm that the new concept is valid

Ongoing experiments

We have 2 new RHWP units for our active experiments:

• MAMBO-1 on the IRAM 30m telescopePico Veleta, Spain (3000 m amsl)larger telescope: 30 m dishlonger wavelength: receiver MAMBO-1@ 1.2 mmmore sensitivity: MAMBO-1 has 37 bolometershigher resolution: 11” beam

• LABOCA on APEXbetter site: Llano de Chajnantor, Chile (5,100 m amsl)submillimeter telescope: 12 m dish, 15 m rmswavelength: 850 mlarge array: 295 bolometershigh resolution: 18” beamlarger array: 11’ fast mapping speed: 2’/shigher sensitivity: 1 square degree in 1.5 hour, 125 mJy rms noise level

Hints for discussion

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

PolKaa tunable polarimeter for (sub)mm

bolometer arrays

Giorgio SiringoBolometer Development

Millimeter & Submillimeter Astronomy GroupMax-Planck-Institut für Radioastronomie (MPIfR)

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

BPol Workshop - October 25-27, 2006

PolKa = Polarimeter für Bolometer Kameras