Post on 01-Feb-2016
description
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