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GREGORTelescope, AO, BBI
Dirk SoltauKiepenheuer-Institut für Sonnenphysik
CASSDA School, April 20th, 2015
The demand for high spatial resolution
Show the simulations the truth?
Courtesy Oskar Steiner, KIS
Show the simulations the truth?
Solar Tornado
Credits: Wedemeyer-Böhm (2012). Image produced with VAPOR
High Resolution
Diffraction Limited Resolution
http://www.olympusmicro.com/primer/anatomy/numaperture.html
Dλθ 22.1=
Example:
λ = 550 nmD = 1 m
θ = 0.67 µrad = 0.14 arcsec
[rad]
By the way: There is no free lunch
• Number of photons per arcsec2 ∝ T × D2
• Size of the resolution element in arcsec2 ∝ 1/ D2
Strehl
Strehl > 0.6 „good“Strehl > 0.8 „diffraction limited“
GREGOR Modulation Transfer Function(MTF)
1“ 0.5“ 0.1“
Aperture, f-ratio, field of view• Desired resolution at 550 nm : 0.1 arcsec
– D = 1.4 m• Pixel size = 10 µm
– image scale = 0.1 arcsec/20 µm = 5 arcsec/mm– f = 41.2m– f-ratio = f/30
• Number of pixels = 4096– FOV = 200 arcsec
f
1 mm5 arcsec
image scale [arcsec/mm] = ( f[mm] * tan(1“) )-1
= 206270/ f[mm]
Three types of mirror telescopesNewton Cassegrain Gregory
Optical Design 1The Simple Solution
McMath-Pierce, f/54
f=86 m
McMath-Pierce (Lazy Seven, f/54)
D = 0.7 mf = 45 m
f/64
Vacuum Tower Telescope (VTT)
VTT opticallayout
SOLIS: A solar Cassegrain telescope
The Gregory Coudé telescope
Picture taken fromhttp://www.irsol.ch/Poster/ao-poster.pdf
D = 0.45 mf = 25 m
f/55
From Gregory to GREGOR• Has to be shorter than 4 m to fit into dome• Diameter : 1.5 m
• f/# of primary appr. 2• Diffraction limited resolution = 0.08 arcsec
• Central obscuration < 0.3 f/# M2 > 1• Secondary focus F2
FF1F2
Heat load in a solar telescope focus
• Solar power density (max) 0.1 W/cm2
2
10000ionmagnificatdensity power
≈
fD
Power density in GREGOR F1 ≈ 300 W/cm2 !!
In any solar telescope focus:
Optical Design
D = 1.5 mf/40
Power mirrorsRadius of curv. Conic const f/#
M1 -5013 mm -1 f/1.8
M2 -1039 mm -0.306 f/1.2
M3 -2797 mm -0.538 f/4
Foci (FOV = 150 arcsec)f/# Image scale Magn. FOV Power Power dens.
F1 1.8 82 arsec/mm 1.8 mm 1600 W 300 W/cm2
F2 6 23.6 arcsec/mm
3.5 6.3 mm 10 W 30 W/cm2
F3 40 3.6 arcsec/mm 6.6 41.6 mm 4 W 0.3 W/cm2
Scatter diameter:150 µm = 12 arcsec
Optical quality in F1 (FOV = 200“)
Scatter diameter:40 µm = 1 arcsec
30 W/cm2
Optical quality in F2 (FOV = 200“)
Scatter diameter:20 µm = 0.07 arcsec
0.7 W/cm2
Optical quality in F3 (FOV = 200“)
Overview of telescope structure and optical
path
Dr. Reiner Volkmer, Kiepenheuer Institut für Sonnenphysik, Freiburg
Dr. Reiner Volkmer, Kiepenheuer Institut für Sonnenphysik, Freiburg 28
Telescope structure
• Sun heats structure and mirrors open telescope and completely foldable dome (telescope in free air flow). Telescopes with 1.5 m free aperture and evacuated light path are very difficult to build
• full performance at wind speeds up to 20 m/s with relative pointing error (rms): 0.5“ (open loop)
• temperature difference to ambient :+0.2 K < ∆T < -0.5 K
Structure
Dr. Reiner Volkmer, Kiepenheuer Institut fürSonnenphysik, Freiburg 30
Why Silicon Carbide main mirrors?• solar radiation on surface of 1.5 m main mirror: 2000 W• ∆T mirror – ambient temperature should be < 1K (internal seeing)• heating of mirrors is critical !!!• silicon carbide has high thermal conductivity:
K(silicon carbide) ~ 100 x K(Zerodur) • silicon carbide mirrrors can be "thinned" and structured (high stiffness)
– ► light weight mirror (M1 ~ 90 kg) faster reaction on temperature changes
– ► removal of heat on back side• GREGOR: Primary, secondary and tertiary are silicon carbide mirrors
M336 cm2.5 kg
raw
finished
Mirror seeing - Mirror Cooling
• Heat transfer bythermal conductivity:
TAd
Q ∆⋅= λ.
Material λ[W/(mK)]
Air 0.03
Glass 0.76
Cesic 121
Zerodur 1.46
Copper 403
d = thicknessA = area
Example M1:ZerodurD = 30 mmA = 1.7 sqm∆T = 3 K dQ/dt = 250 W
Example F1 heat stop:CopperD = 10 mmA = 0.0005 sqm∆T = 10 K dQ/dt = 200 W
Primary mirror and field stop cooling
Air flowM1 mirror
Nozzle
Heatexchanger
FanHousing
Thermal control system
The enemy
Some atmospheric optics(index of refraction for air)
62 10)22.16.272(1)( −++=
λλn
6106.771)( −=−T
Prn
Wave length dependence of n
T and P –dependence of n
Example : P=1000 mbar, T=293 K → ∆n=10-6 per degree
Some atmospheric optics(turbulence)
viscosity:scale spatial :d
velocity:vdensity:
η
ρη
ρ dvRe⋅⋅
=
3/11)( −∝ kkE
Reynolds number Re: 105, i.e. . Atmosphere is always turbulent and never laminar
Kolmogorov spectrum
Kolmogorov’s theory of turbuklence
van Gogh, „Starry Night“
Some atmospheric optics: structure function
[ ] 3/22211 )()( −=−+= rCrnrrnD nrrn
Dn = Structure function Cn2 = structure constant (unit m-2/3 )
Cn2 is a function of height
Cn2 = 10-17 m-2/3
Cn2 = 10-14 m-2/3 37
D. Soltau, Mai 2000 38
Cn2 profile (Example Hufnagel model)
( )2/120
5
2
),(1500/161000/2
10532
)(15
1
1027
210.2)(
=
+
=
∫
−−−−
km
km
thrhhn
dhhvkm
W
eeeWhhC
D. Soltau, Mai 2000 39
Fried’s Parameter r0
λπ
β
2
)()sec(423.05/3
0
220
=
=
−
∫
k
dhhCkrL
n
5/60 λ∝r
[ ]223/5
0
2 364.0 radDr
Dtilt
=
λσÜbrigens: Allein die Korrektur für tip/tilt halbiert die durch die Turbulenz verursachte Varianz
r0 is a kind of atmospheric “aperture”
Measuring r0 (example)
[ ]223/5
0
2 364.0 radDr
Dtilt
=
λσ
DIMM = „Differential image motion monitor“
Adaptive Optics: The Idea
• Babcock (1953): The possibility of compensating astronomical seeing
Horace Welcome Babcock, 1912 - 2003
Adaptive Optics:An Additional Requirement for a
Telescope Design
We need a pupil image
http://lyot.org/background/adaptive_optics.html
Relay Optics
fast
GREGOR AO System: GAOS
GAOS: How many actuators do weneed?
Subapertur: 10 cm x 10 cm
r0 = 5 cm
r0 = 10 cm
How large is the corrected FOV?
Hr0314.0=θ
Example: r0 = 10 cmH = 2 km
θ = 1.6 10-5 rad = 3 arcsec
Deformable mirror
DM Characteristics•stacked-Piezo, made by CILAS•256 actuators, 196 illuminated•48mm illuminated diameter•5μm stroke•3.2mm actuator pitch•new glueing technology•first resonance frequency > 10 kHz
CILAS DM: 256 actuators
Shack Hartmann WFS
Solar AO• Target: Granulation
– Intrinsiccontrast: 14%
– in telescope 2% bis 5%
– structure sizetypical 2“
Observations mostly done in thevisible and near infrared
Minimum size of subaperture?
1/arcsec
taken from ATST archive 52D. Soltau (KIS), Delft Workshop 21./22.02.1321.02.2013
Bottle neck: The WFS camera
1600 fps
GREGOR AO GUI
54D. Soltau (KIS), Delft Workshop 21./22.02.1321.02.2013
Night time AO performance
Night time performance with AO
FWHM = 0.2 arcsec
Multi ConjugateAO for GREGOR
GREGORF1
F2
F3
F4 Pupil
Back end instruments
• GRIS• GFPI• BBI (Broad Band Imager)
Instrument Floor
BBIGFPI
GRIS
Broad Band Imager
F4
F4
WFS
Collim.
Pupil
Pupil
Filter
Cameraf = 260 mm
Detector 1
BS BS
Detector 2
(PCO 4000)PCO Sensicam
Filter(wheel)
f = 400 mm Cameraf = 486 mm
fromtelescope
Broadband Imager
First Results - BBI
• June 2013, parallel with Sunrise flight
• Courtesy A. Lagg, R. Schlichenmaier, M. Franz
Summary
• GREGOR provides world class observingcapabilities. It is:– A large telescope– at an excellent site– fully equipped with AO and backend instruments– beside an excellent Vacuum Tower Telescope
GREGOR�Telescope, AO, BBIThe demand for high spatial resolutionShow the simulations the truth?Show the simulations the truth?High ResolutionDiffraction Limited ResolutionBy the way: There is no free lunchStrehlGREGOR Modulation Transfer Function (MTF)Aperture, f-ratio, field of viewThree types of mirror telescopesOptical Design 1�The Simple SolutionMcMath-Pierce, f/54McMath-Pierce (Lazy Seven, f/54)Vacuum Tower Telescope (VTT)VTT optical layoutSOLIS: A solar Cassegrain telescopeFoliennummer 18The Gregory Coudé telescopeFrom Gregory to GREGORHeat load in a solar telescope focusOptical DesignPower mirrorsOptical quality in F1 (FOV = 200“)Optical quality in F2 (FOV = 200“)Optical quality in F3 (FOV = 200“)Overview of telescope structure and optical pathTelescope structureStructureWhy Silicon Carbide main mirrors?Mirror seeing - Mirror CoolingPrimary mirror and field stop coolingThermal control systemThe enemySome atmospheric optics�(index of refraction for air)Some atmospheric optics�(turbulence)Some atmospheric optics: �structure functionCn2 profile (Example Hufnagel model)Fried’s Parameter r0Measuring r0 (example)DIMM = „Differential image motion monitor“Adaptive Optics: The IdeaAdaptive Optics:�An Additional Requirement for a Telescope DesignGREGOR AO System: GAOSGAOS: How many actuators do we need?How large is the corrected FOV?Deformable mirrorCILAS DM: 256 actuatorsShack Hartmann WFSSolar AOMinimum size of subaperture?Foliennummer 52Bottle neck: The WFS cameraGREGOR AO GUINight time AO performanceNight time performance with AOMulti Conjugate AO for GREGORGREGORBack end instrumentsInstrument FloorBroad Band ImagerBroadband ImagerFoliennummer 63First Results - BBISummary