Transcript Overview of DKIST (formerly ATST) end-to-end

Polarization Calibration of the Daniel K Inouye
Solar Telescope (DKIST)
formerly Advanced Technology Solar Telescope
David Elmore
Instrument Scientist
National Solar Observatory1
Boulder, CO USA
1 Association of Universities for Research in Astronomy funded by the National
Science Foundation.
• 4-m off axis
Gregorian
• Altitude-Azimuth
mount
• At least 10 mirrors
between the sun and
an instrument
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Polarimetric Techniques & Technology
• Use observations to calibrate mirrors
preceding calibration optics.
Calibration
• Polarization state generation optics at
Gregorian focus to calibrate the relay
optics and polarimeters.
• Polarimeters at each of four
instruments in the Coudé Lab
Polarimeters
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Polarimetric Techniques & Technology
3
ViSP
Coudé Layout
Cryo-NIRSP
VBI
VTF
WFC
DL-NIRSP
4
Visible Spectro-polarimeter
(ViSP): Any three lines
simultaneously between 380nm
and 1100nm
Cryogenic Near Infrared Spectropolarimeter (Cryo-NIRSP):
Individually selectable lines
between 1000nm and 5000nm.
Diffraction Limited Near
Infrared Spectropolarimeter (DL-NIRSP):
Three selectable lines
simultaneously between
500nm and 2500nm.
ViSP
Cryo NIRSP
Visible Tunable Filter:
Individually selectable lines
between 520nm and 860nm.
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VTF
DL NIRSP
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Polarization Calibration Process
• Create a model, a string of Mueller matrices,
that describes polarization of the telescope endto-end.
• Measure intensities for numerous calibration
optics generator states and telescope
orientations to infer parameters of the model
from Gregorian focus to the instruments
• Measure polarization of targets of known
polarization signatures to infer properties of
optics preceding the Gregorian focus
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Polarimetric Techniques & Technology
m(j, coude - az, el, j) = PQj M10 M9 M8M7Rcoude-az M6 M5Rel M4M3C j M2 M1s
Polarization model predicts:
Intensity for each calibration optical
configuration (j), elevation, coudeazimuth angle, and modulator
rotation angle (φ) at a range of
wavelengths.
At least a starting point for higher
order effects, field of view changes,
temporal degradation, …
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Polarimetric Techniques & Technology
Calibration
Polarimeters
7
In order to infer the telescope model from
measurements, simplify the model to reduce the
number of free parameters
• Group mirrors into fewer individual matrices
– M12
– M34
– M56
• Use a simplified matrix description for each of
the groups
• Group final mirrors, instrument optics, and
modulators into a modulation matrix
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Polarimetric Techniques & Technology
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Mirror Groups
m(j, coude - az, el, j) = PQj M10 M9 M8M7Rcoude-az M6 M5Rel M4M3C j M2 M1s
M56
M34
M12
• A string of mirrors with axes crossed or aligned has the matrix form
of a single mirror and is described by retardation, δ, and the ratio of
reflectivities in and perpendicular to the plane of incidence, rs/rp.
éæ rs ö
êçè1+ r p ÷ø
ê
êæ 2 ö
êç1- rs ÷
è rp ø
M =ê
ê 2
ê 0
ê
ê
êë 0
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æ rs ö
ç1- ÷
è rp ø
2
æ rs ö
ç1+ ÷
è rp ø
2
0
0
0
0
rs cos(d )
rp
- rs sin(d )
rp
Polarimetric Techniques & Technology
ù
ú
0
ú
ú
ú
ú
0
ú
rs sin(d ) ú
ú
rp
rs cos(d )ú
úû
rp
9
m(j, coude - az, el, j) = PQj M10 M9 M8M7Rcoude-az M6 M5Rel M4M3C j M2 M1s
Solid = Azimuth
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Dotted = Elevation
Polarimetric Techniques & Technology
Winter, Spring, Summer
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Modulation Matrix
m(j, coude - az, el, j) = PQj M10 M9 M8M7Rcoude-az M6 M5Rel M4M3C j M2 M1s
Oinst
Modulation matrix includes the modulator itself as well
as all polarizing optics from the last telescope rotation
through the instrument.
-- José Carlos del Toro Iniesta, Manolo Collados.
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Polarimetric Techniques & Technology
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m(j, coude - az, el, j) = PQj M10 M9 M8M7Rcoude-az M6M5Rel M4M3C j M2 M1s
Calibration polarization generator configurations.
-- Andrew Skumanich, Bruce Lites, Valentin Martinez Pillet
Clear
Retarder: 0°, 45°, 90°, 135°
Linear polarizer: 0°, 45°, 90°, 135°
Polarizer + retarder: Polarizer 0°, 45°, 90°, 135°,
Retarder = Polarizer ± 45°, 0°
Also determine:
Input Stokes vector
Transmission of retarder.
Transmission of polarizer.
Mount error of retarder relative to polarizer.
Retardation of retarder!
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Polarimetric Techniques & Technology
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Truth: solid
Simple: diamonds
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M1 and M2
• From observations, one must determine two parameters, δ, and the
ratio of reflectivities in and perpendicular to the plane of incidence,
rs/rp.
éæ rs ö
êçè1+ r p ÷ø
ê
êæ 2 ö
êç1- rs ÷
è rp ø
M =ê
ê 2
ê 0
ê
ê
êë 0
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æ rs ö
ç1- ÷
è rp ø
2
æ rs ö
ç1+ ÷
è rp ø
2
0
0
0
0
rs cos(d )
rp
- rs sin(d )
rp
Polarimetric Techniques & Technology
ù
ú
0
ú
ú
ú
ú
0
ú
rs sin(d ) ú
ú
rp
rs cos(d )ú
úû
rp
14
M1 and M2
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Polarimetric Techniques & Technology
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Correlation Method: Zeeman effect in magnetically sensitive absorption lines
éæ rs ö
êçè1+ r p ÷ø
ê
êæ 2 ö
êç1- rs ÷
è rp ø
M =ê
ê 2
ê 0
ê
ê
êë 0
Figure . Synthetic profiles before and after correcting for Doppler shift. Polarization parameters are
magnified by a factor of five. Black traces are original profiles. Colored curves are Doppler corrected
I(magenta), Q (red), U(green), and V(blue).
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Polarimetric Techniques & Technology
æ rs ö
ç1- ÷
è rp ø
2
æ rs ö
ç1+ ÷
è rp ø
2
0
0
0
0
rs cos(d )
rp
- rs sin(d )
rp
ù
ú
0
ú
ú
ú
ú
0
ú
rs sin(d ) ú
ú
rp
rs cos(d )ú
úû
rp
Correlation Method
M2 M1
Circular to linear crosstalk using the product of
a circular polarization kernel times Q and times
U plotted vs. the kernel times V.
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Polarimetric Techniques & Technology
Mueller Mat rices Using Sky Polarizat ion
3
Rayleigh scattering: Harrington, Kuhn & Hall 2011
l deviat ions in t he
gh model. Obsersion (Pust & Shaw
w et al. 2010).
model is seen in Fige observers locat ion
cal t ime. T he solar
he t elescope point geomet ry in Figarizat ion (δm ax ) in
gle (γ) of 90◦ . T he
ree of polarizat ion
(6)
t he Rayleigh sky
e scat t ering plane,
on wit h respect t o
t elescope. T he law
reaks down at t he
mply calculat e t he
scope point ing and
on of t he polarizacompared wit h our
Haleakala on Jan-
surement s obt ained
nearby sit e and at
hlberg March
et al.2014
2009)
mum degree of po-
F ig. 2.— T his Figure shows t he sky polarizat ion modeled for
Haleakala at 3:00 UT on January 27t h 2010. T he degree of polarizat ion (δ) at all t elescope point ings wit h δm a x scaled t o 100% is
in t he t op left panel. T he scat t ering angle wit h respect t o t he sun
is in t he t op right panel. T he solar alt it ude is 15◦ and t he solar azimut h is 243◦ . T he calculat ed q and u input s as seen by t he A EOS
alt it ude-azimut h t elescope are on t he bot t om t wo panels. + Q is
defined as E-field vibrat ions along t he + A lt it ude direct ion. + U is
defined as E-field vibrat ions along t he + A lt it ude, + A zimut h direct ion. A ll panels show st ereographic proj ect ions t o t he observed
sky wit h t he Zenit h in t he cent er of t he circle. Nort h, East , Sout h,
West are on t he perimet er of t he circle wit h Nort h up and West
right .
Polarimetric Techniques & Technology
Rayleigh scattering
X
X
X
X
• Measure sky polarization including locations
with the scattering angles at ±45° (±U) to the
azimuth of the telescope and therefore plane of
incidence on M1M2.
• rs/rp is determined from the measured offset
seen 0° (Q)
• δ is determined by the amount of measured
circular polarization.
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Polarimetric Techniques & Technology
Coronal Polarization:
• Rayleigh scattering
goes as λ-4 At 4μ
the K-corona is
brighter than the
sky!
• rs/rp is determined from orientation of linearly polarized
light, should be tangent to the limb
• δ is determined by the amount of measured circular
polarization.
March 2014
Polarimetric Techniques & Technology
DKIST Polarization Calibration Process
• Create an end-to-end polarization model of the
telescope and instruments.
• Measure intensities for numerous calibration
optics generator states and telescope
orientations to infer parameters of the model
from Gregorian focus through each polarimeter
• Perform polarization measurements of targets of
known polarization signatures to infer properties
of optics preceding the Gregorian focus
March 2014
Polarimetric Techniques & Technology
Division of time: High modulation efficiency
simultaneously over a 5:1 wavelength range
4k x 4k field of view: Division of wave front a
problem.
Diffraction limited 4-m telescope: Division of
aperture a problem.
Full Stokes polarimetry at a continuous range of
wavelengths in high spectral resolution: Spectral
modulation a problem.
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Polarimetric Techniques & Technology
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m(j, coude - az, el, j) = PQj M10 M9 M8M7Rcoude-az M6 M5Rel M4M3C j M2 M1s
Rotating Poly-Chromatic Modulator designed
by Roberto Casini consisting of three quartz
compound zero order wave plates at unique
angles producing an elliptical retarder.
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Using efficiency methodology published by Jose Carlos del Toro
Iniesta and Manolo Collados, sampled over 20 states per rotation (in
this example) efficiency vs. wavelength is:
100%
90%
80%
100%
90%
80%
March 2014
Polarimetric Techniques & Technology
100%
90%
80%
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