Transcript TPF-C Optical Requirements Stuart Shaklan TPF-C Architect

National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
TPF-C Optical Requirements
Stuart Shaklan
TPF-C Architect
Jet Propulsion Laboratory, California Institute of Technology
with Contributions from
Luis Marchen, Oliver Lay, Joseph Green, Dan Ceperly, Dan Hoppe,
R. Belikov, J. Kasdin, and R. Vanderbei
TPF-C Coronagraph Workshop
September 28, 2006
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 1
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
•
•
•
•
•
Overview
Flowdown of science requirements to engineering requirements
Meeting the requirements: TPF-C FB-1 Error Budget
Optical surface requirements
– Related to wave front control system and bandwidth
– Effect of uncontrolled spatial frequencies (frequency folding)
– Related to finite size of the star
Image plane mask surface roughness requirements
Thermal/Dynamics requirements
– Sensitivity of different coronagraphs to low-order aberrations
– System requirements
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 2
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
High-Level Requirements
•
SCIENCE: Detect 30 potentially habitable planets assuming hearth =1.
– Also measure orbital semi-major axis, perform spectro-photometry,
detect photons from 0.5 – 1.1 um, perform spectroscopy.
•
Ongoing MISSION STUDIES have been used to derive engineering
requirements from science requirements.
– For the Flight Baseline 1 (FB-1) study, emphasis was first placed on
the detection requirement.
•
ENGINEERING: The Mission Studies reveal that the detection
requirement is satisfied with IWA = ~65 mas and SNR=5 at Dmag =
25.5 (Contrast = 6.3e-11), using a100 nm wide channel.
– Orbit, spectro-photometry, and spectroscopy requirements will likely
drive us to a deeper contrast requirement.
•
FLOWDOWN:
– Control Scattered light to below Zodi + ExoZodi, ~ 1e-10
– Measure, estimate, or subtract speckles to 5x below Dmag = 25.5
or 1.2e-11
– Work at 4 l/D with D=8 m (equiv to 2 l/D for D=4 m).
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 3
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Speckle Floor, Stability
CONTRAST
CONTRAST STABILITY
STATIC BUDGET
Is = Static Contrast
Wave Front Sensing
Wave Front Control
Gravity Sag Prediction
Print Through
Coating Uniformity
Polarization
Mask Transmission
Stray Light
Micrometeoroids
Contamination
JPL Coronagraph Workshop
Contrast = Is + <Id>
Stability = sqrt(2Is<Id> + <Id2>)
DYNAMIC BUDGET
Id = Dynamic Contrast
Pointing Stability
Thermal and Jitter
Motion of optics
Beam Walk
Aberrations
Bending of optics
Sept. 28-29, 2006 – S. Shaklan– 4
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Static vs. Dynamic
Contrast Stability
-12
x 10
-12
11
Log 10 Static Contrast
-11.8
10
-11.6
9
-11.4
8
-11.2
7
6
-11
TPF-C Baseline
Error Budget
-10.8
5
4
-10.6
3
-10.4
Speckle variability exceeds
requirement in this region.
-10.2
2
1
-10
-13
-12.5
-12
-11.5
-11
-10.5
-10
Log10 Dynamic Contrast
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 5
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
System Static Error Budget
STATIC ERROR BUDGET COMPONENTS
Polarization
Design Pol
Coating Uniformity
Optical Surface Quality
Surface Wavefront
Primary Mirror
Contamination
Secondary Mirror
Fold Mirrors
Wave Front Sensing
Image Plane Chromatic Blurring
Frequency Folding
Reference Beam Amp/Phase
Pupil Plane Chromatic Calib
DMs
Finite Size Star
Coherent (light loss)
Primary Mirror
Surface Wavefront
Primary Mirror
Secondary Mirror
Other Optics
Secondary Mirror
Fold Mirrors
Partially Coherent
Other Optics
Reflectivity Uniformity
Primary Mirror
Secondary Mirror
DMs
Primary Mirror
Secondary Mirror
Other Optics
Other Optics
Reflectivity Uniformity
Primary Mirror
Secondary Mirror
Fold Mirrors
DMs
Other Optics
VISIBLE NULLER
Fiber Array
Cross Talk
WF Flatness
Foc. Lenslet
Fiber Array
Output Lenslet
PUPIL MAPPING
Pupil Distortion
Primary Mirror
Secondary Mirror
Fold Mirrors
DMs
Other Optics
Fold Mirrors
DMs
Other Optics
BAND LIMITED / VORTEX
Image Plane Mask
Differential Beam Splitter
Differential Compensators
Differential Coatings
Polarization
Birefringence
Material
Mounting
Pupil Rotation
Differential Incidence Angle
Pupil Plane Mask
Random Errors
OD profile
Surface roughness
Systematic Errors
OD profile
Dispersion
SHAPED PUPIL
Random Errors
OD profile
Surface roughness
Systematic Errors
OD profile
Phase(OD)
Edge Resolution
EXTERNAL OCCULTER
Phase(OD)
Edge Resolution
Polarizaiton
Polarization
Birefringence
Deployment
Design
Material
Gap Transmission
Mounting
Micrometeoroids
Solar Illumination
Dispersion
OD(lambda)
Phase(lambda)
Edge Shape, Sharpness
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 6
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
System Thermal/Dynamic Error Budget
<Id>
5.14E-12
Thermal Bending of Optics
8.60E-13
Structural Deformation
1.49E-12
Ideal Mask
Reserve=
8.55E-13
Jitter Bending of Optics
8.60E-13
2.00
Leakage Due to Jitter
6.33E-13
Ideal Mask
Reserve=
8.55E-13
Leakage Due to Thermal Effects
8.62E-13
Structural Deformation Beam Walk
Medium Changes
6.22E-13
2.00
Mask Errors
Reserve=
5.19E-15
Structural Deformation Beam Walk
Slow Changes
4.73E-13
Mask Errors
Reserve=
2.00
5.19E-15
Structural Deformation aberrations
Ideal Mask (Medium Changes)
2.75E-17
Structural Deformation Beam Walk
Fast Changes
1.13E-14
Structural Deformation Beam Walk
Medium Changes
3.49E-13
Structural Deformation Beam Walk
Fast Changes
6.83E-15
Structural Deformation aberrations
Mask Errors (Medium Cnages)
1.64E-17
Structural Deformation aberrations
Ideal Mask (Fast Changes)
2.45E-19
Structural Deformation aberrations
Mask Errors (Fast Cnages)
1.59E-19
Image Position Offset and Jitter Ideal Mask
Reserve= 2.00
9.24E-14
Image Position Mask Errors
Reserve= 2.00
5.46E-13
JPL Coronagraph Workshop
Rigid Body Pointing Compensated by Sec
Reserve= 2.00
2.84E-15
Rigid Body Pointing Compensated by DM
Reserve= 2.00
1.26E-12
Rigid Body Pointing (Uncompensated)
Reserve= 2.00
2.92E-14
Sept. 28-29, 2006 – S. Shaklan– 7
0.00
Where do TPF-C surface
requirements come from?
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Axiom: Given a pair of ideal DMs, a stable telescope, and monochromatic
light, all energy in the dark hole can be completely removed.
- Independent of the wave front quality of the optics.
What happens in broad-band light?
- Phase and amplitude variations across the pupil Fp(l)
- Phase and amplitude dependence of DM correction Fc(l)
Contrast
If Fp(l)≠Fc(l)
Residual
Contrast
lo-Dl/2
JPL Coronagraph Workshop
lo
Fp(l) comes from
unpropagated (‘direct’)
terms, and propagated
energy. Both must be
considered.
lo+Dl/2
Sept. 28-29, 2006 – S. Shaklan– 8
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Michelson Wave Front Control
y
P
D
Pupil Conjugate
q
z
a=4ps/l
Phase control: 1/l
Ampl. Control: 1/l2
Collimated light reflects from an optic having a periodic surface deformation
of r.m.s. height s. The light propagates a distance z to the pupil (or conjugate
plane) where the wave front correction system is located. The system shown is
a dual deformable mirror (DM) corrector in a Michelson configuration. The
DMs control both amplitude and phase.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 9
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Sequential WFC
D
DMp
zDM
DMnp
Pupil Image
Phase control: 1/l
Ampl. Control: l independent
Two DMs are separated by distance zDM. One is at the pupil. The pupil DM
controls phase. The non-pupil DM adjusts its phase, which propagates to the
pupil and becomes wavelength-independent amplitude.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 10
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Visible Nuller
DM element
tip-tilt
Output power  q
SM Fiber
q
llong
Coupling vs. frequency
DI (n ) 2n

1
DI (n o ) n o
lshort
The factor of 2 scaling with frequency arises
from the combined scaling of both the
image and fiber mode with frequency.
Phase control: 1/l
Ampl. Control: 1/2l
JPL Coronagraph Workshop
Coupling vs. tilt
I
DI(no)
DI(n)
no coupling
n coupling
q
A segmented-DM is matched to a lenslet array that couples light into
a single-mode fiber optic. DM-element tilt adjusts the coupling
efficiency, resulting in a change in the output light level.
Sept. 28-29, 2006 – S. Shaklan– 11
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Propagation Kernel
eia  1  ia
a  2a N cos  2p yN / D   N 
a
Image Plane
Pupil Plane
Ampl 
2
(rN  a N )
2
q  Nl / D
D
z
D/N
d  z 1  cos q  
d
Ampl  1
N 2l 2
z
2D2
r = reflectivity
N 2l
Diffracted component phase delay is   2p d / l  p z 2
D
E  1

2r  2r

cos(2p yN / D   )  i 2a cos(2p yN / D   )  ei
2
 2

 r r  p zl N 2 2 4p 2 szN 2 4p s 2p 3 sz 2 l N 4 p rzl N 2 
E  
,



 
2
2
4
2
2
4
D
D
l
D
2
D




  Er  Er , p 2  Es , p , Es  Es , p 2  Er , p 
  E A , E 
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 12
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Direct and Propagated Terms
Perturbation
Name
Er  r / 2
Ampl. non-uniformity
Es, p  4p 2 szN 2 / D2
Phase (surface) to ampl.
Es  4p s / l
Surface figure
Propagation Effect l-Dependence Michelson or VN
Sequential
no
Ampl.
0
Limits refl. PSD
Controlled
1st order
Ampl.
0
Limits surf. PSD
Controlled
no
Phase
1/l
Controlled
Controlled
Phase to phase
Es , p 2  2p 3 sz 2 l N 4 / D 4
2nd order
Phase
l
Limits surf. PSD
Ampl. to phase
Er , p  p rzl N 2 / 2 D 2
1st order
Phase
l
Limits refl. PSD
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 13
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
TPF-C Layout
SM
PM
M4
M3
DMcol
M3
Cyl2
Cyl1
CDM
and PM Cyl1
SM
DMcol
Cyl2
Image-space images of the optics
Final beam is collimated at the exit pupil. All optics appear to have
the same diameter as seen from the exit pupil.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 14
M4
Surface Height Requirements
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
for R=6.3 and C = 1e-12 per optic
Surface Requirement
Michelson
and Visible
Nuller
Surface
Requirement
(Michelson)
10
10
Surface Requirement
Sequential
Surface Requirement
(Sequential)
3
10
2
10
3
Secondary
DMcol
2
10
1
DMcol
10
10
10
0
DMcol
Dl=50 nm
-1
M4
-2
rms Surface Height (nm)
rms Surface Height (nm)
Secondary
10
10
1
0
M4
10
10
-1
10
EUV
-3
DMcol
Dl=200 nm
-4
10
JPL Coronagraph Workshop
0
DMcol
Dl=200 nm
-2
EUV
10
DMcol
Dl=50 nm
1
10
Cycles/aperture
10
10
-3
-4
10
0
1
10
Cycles/aperture
Sept. 28-29, 2006 – S. Shaklan– 15
Reflectivity Uniformity Requirement
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
10
rms Reflectivity variation
10
10
10
for R=6.3, C=1e-12
Reflectivity Uniformity Requirement for C=1e-12
-1
Secondary
Control authority
surface limit
-2
Limited by ampl.-tophase prop.
Collimator
-3
Control limit for
30 nm piston, DM is
3 m from pupil
-4
M4
Limited by direct reflectivity.
10
10
Michelson
Requirement
Michelson
and Visible
Nuller Requirement
-5
We believe that the state-of-the-art in large optics coatings is
about 0.5% r.m.s., with a 1/f3 PSD. This leads to ~ 1e-11
contrast at 4 cycles/aperture (worse at 2 cycles/aperture).
-6
10
0
JPL Coronagraph Workshop
10
Cycles/aperture
1
Sept. 28-29, 2006 – S. Shaklan– 16
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Finite Size Source
DM compensation is
sheared for an off-axis
element of the target.
D
DMp
zDM
DMnp
Pupil Image
Two DMs are separated by distance zDM. One is at the pupil. The pupil DM
controls phase. The non-pupil DM adjusts its phase, which propagates to the
pupil and becomes wavelength-independent amplitude.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 17
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Contrast Due to Finite Size Source
1  2p x N 
C 
2
D 
 x  az (
JPL Coronagraph Workshop
Dp
Db
)
2
C = Contrast
 = r.m.s. wavefront (radians)
or r.m.s. (reflectivity/2)
x = beam shear
N = cycles/aperture
D = beam diameter
a = Source radius
z = effective distance of optic
from pupil
Dp = pupil diameter
Db = beam diameter
Sept. 28-29, 2006 – S. Shaklan– 18
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Surface Height Requirements
for Finite Size Star (1.7 mas diam.), C = 1e-12 per optic
Surface Requirement
Michelson
and Visible
Nuller
Surface
Requirement
(Michelson)
10
10
Surface Requirement
Sequential
Surface Requirement
(Sequential)
3
10
2
10
3
Secondary
DMcol
2
10
1
Secondary
DMcol
10
10
0
DMcol
Dl=50 nm
-1
M4
10
M4
-2
rms Surface Height (nm)
rms Surface Height (nm)
Secondary
10
10
1
Secondary
0
M4
10
10
-1
M4
-2
DMcol
Dl=200 nm
EUV
10
10
EUV
-3
DMcol
Dl=200 nm
-4
10
JPL Coronagraph Workshop
0
DMcol
Dl=50 nm
1
10
Cycles/aperture
10
10
-3
-4
10
0
1
10
Cycles/aperture
Sept. 28-29, 2006 – S. Shaklan– 19
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
10
rms Reflectivity variation
10
10
10
10
10
Reflectivity Uniformity Requirement
for Finite Size Star (1.7 mas diam.), C = 1e-12 per optic
Reflectivity Uniformity Requirement for C=1e-12
-1
Secondary
Control authority
surface limit
-2
PM & SM
Collimator
-3
Control limit for
30 nm piston, DM is
3 m from pupil
-4
Requirement on PM & SM for
sequential controller, with znp=3 m
from the pupil
M4
Michelson
Requirement
Michelson
and Visible
Nuller Requirement
-5
-6
10
0
JPL Coronagraph Workshop
10
Cycles/aperture
1
Sept. 28-29, 2006 – S. Shaklan– 20
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Preferred DM Configuration
Collim.
CDM M1
M2 DMnp,1
DMp
DMnp,2
Cass.
Focus
1
f1=2.5
f2=2.5
1
zDM=3
zDM=3
3-DM fully redundant system. This diagram depicts an
unfolded layout that provides for 2 non-pupil DMs placed zDM=3
m from the pupil DMp. A unity magnification telescope images
the coarse DM pupil plane CDM to DMp (dashed line). The
design provides 1 m between CDM-M1 and M2-DMnp,1 to fold
the beams at a shallow angle.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 21
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
LESSON 1
• Use a sequential wave front controller.
–
–
–
–
Relaxes optical surface requirements
Increases the useful size of the dark hole
Allows a wider optical bandwidth
Relaxes coating requirements on PM and SM to within state-of-theart
– Provides redundancy
•
A Michelson controller, and fiber spatial-filter amplitude controller make
broad-band amplitude control very challenging.
– Pushes Silver coating beyond state-of-the-art
– Is Aluminum coating uniformity sufficient?
• Aluminum is desired on PM, SM, and M3 to enable general
astrophysics.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 22
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Frequency Folding: Uncontrolled High Spatial
Frequencies Appear in the Dark Hole
The previous charts addressed controllable spatial frequencies – those below
the DM Nyquist frequency.
Give’on has shown that frequency folding terms scatter light into the dark
hole.
Phase in the pupil:

    4p sm / lo  sin(2p xm / D  q m )
m0
Field in the pupil:
E ( x)  ei  1  i   2 / 2
 4p sm 
1  4p 
 1  
sin(2
p
xm
/
D

q
)




m
2  lo 
m  0  lo


Ideal diffraction,
removed by coronagraph
Scatter removed by DM,
up to N cycles across
the dark hole
JPL Coronagraph Workshop
2


 s s
n 0 m0
n m
sin(2p xm / D  q m )sin(2p xn / D  q n )
Mixing of spatial frequencies. We are
concerned with |m-n|<N /2.
2
These pure-amplitude terms  1/ l .
Sept. 28-29, 2006 – S. Shaklan– 23
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Frequency Folding Residual
The Michelson controller has 1/l2 amplitude dependence and completely
removes the light.
The Visible Nuller fiber array does not pass spatial frequencies above N/2. The
frequency folding problem is eliminated.
The sequential controller has l-independent amplitude control. The resulting
contrast in the dark hole is:
1  4p 
C ( ) 


6 R 2  lo 
JPL Coronagraph Workshop
4


m N / 2
PSDm PSDm 
Sept. 28-29, 2006 – S. Shaklan– 24
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
JPL Coronagraph Workshop
Frequency Folding Contrast
for R=6.3, Sequential DMs (96 x 96)
Sept. 28-29, 2006 – S. Shaklan– 25
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
LESSON 2
• Uncontrolled high-spatial frequencies look manageable.
– Existing optics lead to acceptable frequency folding
• What happens when we light-weight the PM???
– Requires large format DM
– Becomes an issue for bandwidth >> 100 nm
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 26
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Image Plane Mask errors
Static contrast
Mask error
Random
Spatially random variations in
mask transmission amp and phase
Systematic
Variations in mask transmission amp and
phase that are correlated with mask pattern
Eout  Ein M  L
  E0  DE  M 0  DM   L
  E0 M 0  E0 DM  DEM 0  DE DM   L
Unaberrated input field with mask errors
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 27
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Gaussian error, monochromatic
1
Unaberrated sombrero function E0
Gaussian mask error DM at ~ 4l / D
550 nm
0.8
E field
•
•
0.6
0.4
0.2
0
-0.2
-2
0.04
E field error exiting mask = E0DM
0
1
2
3
4
5
6
-7
x 10
0.02
E field
•
-1
0
-0.02
-0.04
-2
-1
0
1
2
3
4
5
-3
Diffracted by Lyot stop
E0DM *L
Perfect DM correction (dotted line)
6
E field
•
•
•
6
-7
x 10
x 10
4
2
0
-2
-4
-6
-2
-1
0
1
2
3
4
Angular offset / rad
JPL Coronagraph Workshop
5
6
-7
x 10
Sept. 28-29, 2006 – S. Shaklan– 28
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Gaussian error, broadband
1
•
Two wavelengths to illustrate
broadband case
Blue sombrero function is
compressed
550 nm + 510 nm
0.8
E field
•
0.6
0.4
0.2
0
-0.2
-2
E field at mask exit is quite different
at 510 nm
E field
•
-1
0
1
2
3
4
5
6
-7
0.04
x 10
0.02
0
-0.02
-0.04
-2
-1
0
1
2
3
4
5
-3
6
•
DM correction still perfect for 550
nm, but compressed for 510 nm
DM correction is completely
inappropriate for 510 nm
x 10
4
E field
•
6
-7
x 10
510 nm error before
DM correction
510 nm after
DM ‘correction’
2
0
-2
-4
-6
-2
DM ‘correction’
@ 510 nm
-1
0
1
550 nm error
and correction
2
3
4
5
6
-7
Angular offset / rad
JPL Coronagraph Workshop
x 10
Sept. 28-29, 2006 – S. Shaklan– 29
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Dependence on error spatial scale
for a 100 nm bandpass 500-600 nm, evaluated at 4 l/D
Mask error
scale size (FWHM)
Rms mask error
for 10-11 contrast
•
Simple 1-D analysis used to predict
contrast in image plane from a grid of
random Gaussian mask errors
fl / D
F/60
2
60 mm
91 pm
•
Light scattered from both very
small features is blocked by Lyot stop
1
30 mm
31 pm
•
Large scale errors are effectively
controlled over a broad band.
1/2
15 mm
24 pm
1/4
7.5 mm
27 pm
Large
•
Most sensitive to scales
comparable to sidelobes of
sombrero function:
1
1/8
4 mm
38 pm
0.8
0.6
Small
1/16
2 mm
50 pm
0.4
0.2
0
-0.2
-2
-1
0
1
2
3
4
5
6
-7
x 10
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 30
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
•
•
•
Mask error PSD requirement
Each component has different characteristic spatial scale
Each represents 10-11 contrast
Overall contrast can be suballocated to different scales to match actual PSD of
mask errors
Period = 100 mm
Period = 30 mm
Overall surface r.m.s. ~ 1
A for scales 2 – 60 um.
91 pm rms (60 um scale size)
No
requirement
31 pm rms
24 pm rms (15 um scale size))
sum
27 pm rms
38 pm rms
50 pm rms (2 um scale size)
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 31
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
LESSON 3
• If you’re going to put a transmissive mask in the image
plane, it should have <1 A rms for spatial scales up to 2 lF#
– Due to inherent scaling of spatial frequency with wavelength in the
image plane
– A mask-leakage error looks like a planet – it does not scale with
wavelength.
– Calibrate by rotating the mask, but still requires 1 A rms to keep
scattered light level near 1e-11.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 32
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
•
•
•
•
Thermal/Dynamics Error Budget
Observing Scenario
Coronagraph sensitivity to Low-Order Aberrations
Control systems
Key Requirements
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 33
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Observing Scenario
Scattered Light must be stable to
~ 1e-11 during this time
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 34
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
JPL Coronagraph Workshop
Aberration Sensitivity 1
Mask Throughput
Sept. 28-29, 2006 – S. Shaklan– 35
Aberration Sensitivity 2
Contrast Sensitivity Curves
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Evaluated at 4 l/D
Coma, 4 l/D
Coma, 4 l/D
Coma, 3 l/D
Focus, 3 l/D
Focus, 4 l/D
Focus, 4 l/D
Linear dual-shear VNC aberration sensitivity
and Lyot throughput are identical to a linear 4th
order mask of the form T = 1-cos(x). Sensitivity
is almost identical to 1-sinc2(x).
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 36
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
JPL Coronagraph Workshop
Aberration Sensitivity 3
Allowed WFE
Sept. 28-29, 2006 – S. Shaklan– 37
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
ASTIG
SPHERICAL
JPL Coronagraph Workshop
Aberration Sensitivity 4
Pupil Mapping Sensitivity Curves
TILT
FOCUS
COMA
TREFOIL
ASTI2
Sept. 28-29, 2006 – S. Shaklan– 38
Aberration Sensitivity 5
Pupil Mapping Sensitivity Curves
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Pupil Mapping,
2 lambda/D
COMA
BL4, VNC
4 lambda/D
10-8
Pupil Mapping,
4 lambda/D
Shaped Pupil,
4 lambda/D
JPL Coronagraph Workshop
BL8,
4 lambda/D
Sept. 28-29, 2006 – S. Shaklan– 39
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
•
•
•
•
Open-Loop Aberration Sensitivity Summary
The 8th-order null of a properly built BL8 provides orders-of-magnitude
reduction to low-order aberrations.
Working at 4 l/D, the mask sensitivity to aberrations increases in order:
– BL8, Shaped pupil, Pupil Mapping, BL4/VNC
– BL4/VNC is 100 x more sensitive to aberrations than BL8 (C=1e-12)
– OVCn behaves like 2nth null (OVC4 = 8th order null). Still studying the
tradeoff between sensitivity and throughput.
Working at 3 l/D increases aberration sensitivity by an order of
magnitude.
– 3x tighter WF tolerance to work at 3 l/D with BL8
Working at 2 l/D is harder yet – BL8 throughput too low, so must go to
BL4/VNC, OVC2 or OVC4 (?), or pupil mapping.
– This is 1000x more sensitive to aberration than BL8 at 4 l/D.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 40
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
•
•
•
Thermal/Dynamic Error Budget
Low-order aberrations arise by
– Thermal deformation and misalignment of optics
– Jitter induced deformation and misalignment of optics
– The BL8 mask at 4 lambda/D is quite insensitive to these.
– BL4/VNC are the most sensitive
Beam Walk (shearing of spatial frequencies) is the same for all
coronagraphs.
– If planet light is transmitted at x lambda/D, then a spatial frequency
of x cycles/aperture is also transmitted.
– Beam walk is mitigated by
• Control of optics positions: secondary mirror + FSM
• Quality of optics
Beam walk drives the optical surface quality at a few cycles/aperture.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 41
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
•
•
Control Systems
3-tiered pointing control
– Rigid body pointing using reaction wheels or Disturbance-Free
Payload
– Secondary mirror tip/tilt (~ 1 Hz)
– Fine-guiding mirror (several Hz)
PM-SM Laser Metrology and Hexapod
– Measures and compensates for thermal motion of secondary
relative to primary.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 42
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Key Dynamics Requirements
PM shape: (Thermal and Jitter)
z4=z5=z6=z8=z10=0.4 nm
z7=0.2 nm, z11=z12=5 pm
z
Secondary:
Thermal: Dx=65 nm,
Dz=26 nm,
tilt=30 nrad
Jitter: 20x smaller
Laser metrology:
DL=25nm
Df/f=1x10-9
Mask centration: Mask error =
Fold mirror 1:
offset=0.3 mas
5e-4 at 4 l/D
rms static surf =0.85nm
amplitude=0.3mas
Thermal: 10nrad, 100 nm
4 mas rigid
Jitter: 10 nrad, 10 nm
body
pointing
Figure 5. We identify the major engineering
requirements to meet the dynamic error
budget. Thermally induced translations lead
to beam walk that is partially compensated
by the secondary mirror. Jitter is partially
compensated by the fine guiding mirror.
Coronagraph optics motion:
Thermal:10nrad, 100nm
Jitter: 10 nrad, 10 nm
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 43
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
•
•
•
•
Changes from Baseline
Baseline design assumes BL8 mask.
– Relatively insensitive to low-order aberrations.
Baseline observing scenario is:
– Difference two images made at 30 deg LOS ‘dither’ positions
– No DM reset for several hours during this time
If we switch to BL4, VNC (and to a lesser extent pupil mapping and
shaped pupil), and if we keep the same observing scenario
– We can NOT move secondary mirror to compensate tip-tilt because
moving the secondary introduces significant low-order aberration
– We must therefore maintain very strict pointing accuracy – sub milliarcsec – on the telescope
– We also tighten primary mirror bending stability by orders of
magnitude.
Going to 2 lambda/D with pupil mapping requires even tighter
tolerances.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 44
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
LESSON 4
• Working at 2 or 3 l/D is much, much harder than 4 l/D.
Breakthroughs in wave front control, optical surface quality,
and a change in observing paradigm are needed.
•
– Single-digit picometer wave front control for low-order aberrations
– Sub-pm control of spherical aberration and higher order terms
– Wave front control that is faster than the rigid body pointing errors
• Or, require extremely tight rigid-body pointing
Hopefully we will hear some ideas on how to do this tonight and
tomorrow.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 45
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
•
•
•
•
•
Summary
Design Reference Mission modeling provides flow down of science requirements to
engineering requirements.
Optical Surface Requirements
– We have a good handle on surface height and reflectivity uniformity requirements
through the system.
– The requirements are imposed by
• Wavelength-dependence of scatter vs. compensation
• Finite size of the star
• Thermal/Dynamic beam walk
– High-spatial frequency errors on large mirrors appear to be acceptable for 100
nm bandwidth
– Correction beyond ~ 25 cycles/aperture does not look feasible (but maybe can
live with reduced performance at large working angles).
Image plane mask requirements
– We have a good handle on the PSD of random mask transmission errors.
– Superpolish surfaces (<1 Angstrom r.m.s.) are probably adequate.
Stability Requirements
– Thermal and jitter requirements are well understood.
– Modeling described in the FB-1 report and STDT report shows that the required
stability can be achieved assuming an 8th-order band limited mask at 4 l/D.
Smaller IWA using masks that are more sensitive to aberrations requires a new
approach to WFS/C, one that meets picometer stability requirements and 1e-11
calibration of speckles.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 46
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Pointing Control
Disturbance
Rigid Body
Pointing Control
PSD Models
4 mas
Secondary
2ndry Beam Walk
C-Matrix
Dx
CBW
FGM Beam Walk
C-Matrix
Dx
CBW
Telescope Beam
Walk C-Matrix
Dx
CBW
0.4 mas
Telescope Model
MACOS
FGM
Contrast
0.04 mas
Telescope
Figure 2. Pointing control. The CEB assumes a nested pointing control system. Reaction wheels and/or a Disturbance Reduction System control rigid
body motions to 4 mas (1 sigma). The telescope secondary mirror tips and tilts to compensate the 4 mas motion but has a residual due to bandwidth
limitation of 0.4 mas. A fine guiding mirror in the SSS likewise compensates for the 0.4 mas motion leaving 0.04 mas uncompensated.
JPL Coronagraph Workshop
Sept. 28-29, 2006 – S. Shaklan– 47
National Aeronautics and Space
Administration
Jet Propulsion Laboratory
California Institute of Technology
Contrast Roll Up
Table 4: Rolled up Dynamic Contrast Contributors
Perturbation
Contributor Nature
Structural Defomation Beam Walk
Thermal
Jitter
Aberrations
Thermal
Jitter
Bending of Optics
Aberrations
Thermal
Jitter
Pointing
Beam Walk
Image Motion
Mask Error
SUM
JPL Coronagraph Workshop
Contrast
8.29E-13
6.33E-13
3.28E-14
4.43E-17
8.60E-13
8.60E-13
1.29E-12
9.04E-14
5.46E-13
5.14E-12
Fraction
16.12%
12.31%
0.64%
0.00%
16.72%
16.72%
25.10%
1.76%
10.63%
Sept. 28-29, 2006 – S. Shaklan– 48