DAVINCI Mini-review
Sean Adkins, Renate Kupke, Sergey Panteleev, Mike Pollard
and Sandrine Thomas
April 19, 2010
Acknowledgements
• Science team and collaborators:
– Al Conrad, Mike Fitzgerald, Jim Lyke, Claire Max,
Elizabeth McGrath
• Special thanks to James Larkin and Antonin
Bouchez for valuable advice
• NGAO management team:
– Peter Wizinowich, Rich Dekany, Don Gavel, Claire
Max
2
NGAO Science
•
•
NGAO Science Case Requirements Document (SCRD)
Defines five science cases as “key science drivers” – challenging to
technical performance or setting high priority requirements
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•
High-redshift galaxies
Black hole masses in nearby AGNs
General Relativity at the Galactic Center
Planets around low-mass stars
Asteroid companions
Defines additional cases as “science drivers” – aim is to ensure a wide
range of science is possible
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–
–
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Gravitationally lensed galaxies
QSO host galaxies
Resolved stellar populations in crowded fields
Astrometry science (variety of cases)
Debris Disks and Young Stellar Objects
Giant Planets and their moons
Asteroid size, shape, composition
3
Background
•
NGAO science requirements established a need for certain capabilities in
the SD phase
– Imaging in near-IR and visible
• ~700 nm to 2.4 m
• high contrast coronagraph
– Integral field spectroscopy in near-IR and visible
•
•
•
•
•
spatially resolved spectroscopy for kinematics and radial velocities
high sensitivity
high angular resolution spatial sampling
R ~ 3000 to 5000 (as required for OH suppression and key diagnostic lines)
Improved efficiency
– larger FOV
– multi-object capability
– At SDR
• two imagers and an integral field spectrograph (IFS) on narrow field high Strehl AO
relay (IFS might be OSIRIS)
• 6 channel deployable IFS on the moderate field AO relay with MOAO in each channel
– Build to cost approach required significant changes in scope
4
Constraints & Opportunities
• Constraints
– Cost
• Need to provide capability within a limited amount of funding
• Must understand which requirements drive cost
– Complexity
• Must resist the temptation to add features
• Maximize heritage from previous instruments
• Opportunities
– NGAO offers extended wavelength coverage
• Significant performance below 1 µm, Strehl ~20% at 800 nm
• Substrate removed HgCdTe detectors work well below 1 µm
– Exploit redundancies in compatible platforms – e.g. imager and
IFS
5
Approach to design/build to cost
1. Ensure that the instrument capabilities are well matched to key
science requirements
2. Ensure that the instrument capabilities are matched to the AO
system in order to maximize the science gains
3. Understand which requirements drive cost
4. Resist the temptation to add features
5. Maximize heritage from previous instruments
6. Evaluate ways to break the normal visible/near-IR paradigm of
using different detectors in separate instruments
6
NGAO Parameter Space
Ca II
triplet
Z
1
70%
I
Y
J
H
K
0.9
60%
50%
0.7
Strehl
0.6
40%
0.5
30%
0.4
0.3
20%
Transmission (AO + Tel)
0.8
Keck II LGS AO
0.2
10%
0.1
0
0%
300
800
1300
Wavelength (nm)
1800
2300
NGAO, 140 nm rms
wavefront error
NGAO, 170 nm rms
wavefront error
NGAO, 200 nm rms
wavefront error
Transmission, %
7
Wavelength Coverage
• CCD vs. IR FPA
– Substrate removed HgCdTe detectors work well below 1 µm
– ~20% lower QE than a thick substrate CCD
– Non-destructive readout takes care of higher read noise of IR array
LBNL QE
100.00%
H2RG QE
100.00%
90.00%
90.00%
80.00%
80.00%
Y
J
K
H
70.00%
NGAO
z spec
Transmission, %
Transmission, %
70.00%
60.00%
NGAO z'
50.00%
60.00%
Teledyne min. spec. for
substrate removed
H2RG
50.00%
40.00%
NGAO i'
30.00%
40.00%
NGAO rl
20.00%
NGAO visible
10.00%
30.00%
20.00%
0.00%
NGAO near-IR
0.5
0.6
0.7
0.8
0.9
1
1.1
1.2
Wavelength, m
10.00%
0.00%
0.3 0.4 0.5 0.6 0.7 0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9
2
2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9
3
Wavelength, m
8
Summary of Capabilities
Capability
Wavelength
Coverage
Filters
Spectral Resolution
FOV
Spatial Sampling
Throughput
(instrument only)
Detector
Detector
Performance
Integral Field Spectrograph
Imager
I, Z, Y, J, H, K (0.7 to 2.4 µm)
I, Z, Y, J, H, K (0.7 to 2.4 µm)
Narrowband in I, Z, Y, J, H, K, nominally 5% band
pass per filter, two to four filters as required for each
band
Photometric filter in each
passband, generous selection of
narrow band and specific line
filters similar to NIRC2
~4000
1
≥ 15"
~ 4" x 4" with 50 mas sampling
~ 1" x 1" with 10 mas sampling
3 scales maximum:
 10 mas
 50 to 75 mas, spatial sampling selected to
match 50% ensquared energy delivered
by NGAO narrow field relay
 Intermediate scale, possibly 20 or 35
mas, selected to balance FOV/sensitivity
trade off
~40% (goal)
4096 x 4096 (Hawaii-4RG)
Background limited
≤ λ/2D, possibility of multiple
pixel scales
> 75% (goal, without
coronagraph)
4096 x 4096 (Hawaii-4RG)
Background limited or detector
limited depending on observing
band
9
The DAVINCI Concept
• Imager with on-axis IFS mode
• FOV
• Coronagraph
• Sky background limited performance
10
Imager Sensitivity
Zero points and background magnitudes for DAVINCI imaging
Photometric
Passband
I band photometric
Z band photometric
Y band photometric
J band photometric
H band photometric
K band photometric
Cut-on,
nm
700
818
970
1170
1490
2030
Cut-off,
nm
853
922
1070
1330
1780
2370
CWL, nm
Zero point
776.5
870
1020
1250
1635
2200
27.42
27.24
26.97
27.05
27.07
26.52
Background,
mag./sq. arcsecond
22.13
21.28
17.28
16.04
13.76
14.78
DAVINCI imaging sensitivity
Photometric
Passband
I band photometric
Z band photometric
Y band photometric
J band photometric
H band photometric
K band photometric
Ave. Strehl (170 nm
wavefront error)
15%
22%
33%
39%
59%
79%
Time per
exposure
120 s
120 s
900 s
900 s
900 s
900 s
5
mag.
27.8
27.9
28.0
27.4
26.5
26.7
Time for single exposure to
background limit, mag. = 27
6.7 h
5.6 h
1800 s
560 s
70 s
280 s
11
IFS Sensitivity
Passband
I band spectroscopic
Z band spectroscopic
Y band spectroscopic
J band spectroscopic
H band spectroscopic
K band spectroscopic
Cut-on,
nm
700
855
970
1100
1475
2000
Cut-off,
nm
853
1050
1120
1400
1825
2400
CWL, nm
Zero point
776.5
952.5
1045
1250
1650
2200
26.48
26.90
26.49
26.89
26.40
25.85
Background,
mag./sq. arcsecond
22.13
20.68
17.05
16.33
13.79
14.62
12
DAVINCI
13
14
Imager
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Quality of Pupil Image at cold stop
16
Quality of Pupil Image at cold stop
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Imager
18
Imager Transmission
19
Scale changer magnification
requirements
Lenslet pitch at IFS image plane is 1.2 mm. This compares to
250μ pitch of the OSIRIS lenslets.
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IFS Scale Changer
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Scale changer, JHK
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Scale changer, IZ
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Coronagraph
• Requirements and goals:
ΔJ = 8.5 (or contrast ratio of 4 x 10-4) at 100 mas with a goal of ΔJ = 11 (4 x 10-5) at 0.1"
ΔH = 10 (or contrast ratio of 1 x 10-4) at 200 mas with a goal of ΔH = 13 (6.3 x 10-6) at 1"
ΔK = 10 (or contrast ratio of 1 x 10-4) at 100 mas
• Simple Lyot Coronagraph
• Simulations include
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static aberrations
AO correction
Hexagonal pupil geometry
a 10% transmission Focal plane mask.
• Optimization of the focal plane mask size and the Lyot mask size to
meet the requirements.
24
Coronagraph
• Results
It is possible to meet the
requirements/goals for each band:
H band: (90%, 4 lambda/d)
J band: (82.5%, 8 lambda/d)
K band: (75%, 5 lambda/d)
Sensitivity example for K band, a
companion mag of 24, 5σ sensitivity.
The required integration time goes
from 90s to 300s if we decrease the
Lyot stop to 75% of the full aperture.
A simple Lyot coronagraph meets our requirements if the transmission losses and
small compromises of inner working angles are acceptable.
25
IFS Optical Design: Image Slicer
•
Two concepts for IFS pseudo entrance slit configuration
– Lenslet based slicer
• Similar to OSIRIS
• Well studied performance
– Hybrid lenslet and mirror slicer
• Advantages: higher quality of sampling, no staggering spectra
• Potential drawbacks: cost, impact on image quality and throughput, space
requirements, more demanding requirements for spectrograph collimator and camera
•
Design approach for hybrid slicer
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–
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Formulate requirements
Develop slicer concept and mate to paraxial IFS optics
Understand manufacturability and cost
Refine IFS optics design using virtual slit parameters
• Diffraction grating selection and performance
• Spectral format on detector
• Replace paraxial optics with real optics (TMA concept for example)
– Make a 2nd iteration for hybrid slicer design
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IFS: Hybrid Image Slicer Concept
• Hybrid slicer design drivers
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Spectral and spatial resolution
Image quality
Mating to collimator (and camera)
Available physical space
Technology limitations for small mirror optics manufacturing
• Adopted concept for 80 x 80 spatial samples
40x40
40x40
40x1x10
80x80
4x
8x800
27
40x40
40x40
IFS: Hybrid Image Slicer Optical Layout
• Pupil plane conversion to virtual slit plane.
– Central line symmetry
– Enlarger optics between lenslet and field splitting mirrors
28
IFS: Hybrid Image Slicer Optical Layout
• 4 groups of M1 mirrors (each of 10 slicing) for one sub-field
• Brick-wall arrangement for 10 M2 mirrors
29
IFS: Hybrid Image Slicer Optical
Performance
• Two contributors considered, lenslet and spherical mirrors
– Marginal image size for group 4
– Slit image curvature within 2 pixels
Curvature of 40 sample long sub-slit image
8
7
pixels, spectral direction
Full field pupil images at detector
6
5
4
3
2
1
0
0
5
10
15
20
25
30
35
40
sample# , spatial direction
lens row 10
lens row 20
lens row 30
lens row 40
30
IFS Spectral Format
• Input parameters
– 2 virtual slit configurations
• 8 slit (20 sub-slit each),100 x 180 mm field size at slit plane
• 6 slit (28 sub-slit each),140 x140 mm field size at slit plane (image slicer
performance not checked yet)
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–
–
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Diffraction grating selection using stock groove frequencies
17 pass bands. Each is selected by a filter/rotation angle pair
Set for angle of constant deviation
Spectrum distribution on detector is affected by
• Grating dispersion
• Angle of constant deviation
• Camera optics EFL
31
IFS Spectral Format
• Distribution of spectra at detector (example)
Spectra from 8 slits at CCD
(1-Iband, 2-Zband, 3-Yband, 4-Jband, 5-Hband, 6-Kband)
7
6
band #
5
4
3
2
1
0
-2560
-2048
-1536
-1024
-512
0
pixels
512
1024
1536
2048
2560
1Z
2Z
3Z
4Z
5Z
6Z
7Z
8Z
1Y
2Y
3Y
5Y
6Y
7Y
9Y
4Y
1J
2J
3J
4J
5J
6J
7J
8J
1H
2H
3H
4H
5H
6H
7H
8H
1K
2K
3K
4K
5K
6K
7K
8K
1I
2I
3I
4I
5I
6I
7I
8I
left
right
32
IFS Spectral Resolution
•
•
Spectral resolution for I-band and
Z-band maintains selection of
diffraction gratings (groove
frequency) and conditions of
grating illumination
6 slit configuration is closer to
meet specification
8 slits
6 slits
Passband
G,1/mm
R
G,1/mm
R
Ia
200
2385
272.3
3410
Ib
200
2668
272.3
3840
Za
150
2167
210
3185
Zb
150
2431
210
3598
Ya
165
2730
245
4381
Yb
165
2966
245
4798
Ja
135
2525
180
3531
Jb
135
2778
180
3906
Jc
135
3037
180
4296
Ha
135
3491
150
3966
Hb
135
3735
150
4250
Hc
135
3984
150
4543
Hd
135
4240
150
4844
Ka
100
3490
135
5069
Kb
100
3696
135
5395
Kc
100
3906
135
5732
Kd
100
4121
135
6080
33
IFS: Hybrid Image Slicer Optical Layout:
2nd iteration
• Field magnification function is transferred to scale changer in front of
lenslet
• Diffraction grating magnification allows smaller spacing between
slits (from 25.2 mm to 19.3 mm) thus smaller field at slit plane
• Advantages:
– Smaller incident angles in Y (spectral direction) -> better image quality
– M2 mirrors can be arranged as a single row (no brick-wall)-> easier for
manufacturing
• Problems:
– pupil image at 50 mas scale (1.1 mm dia. vs. 1.2 mm slicing mirror) at
M1 slicer may be too large ( at 1st iteration this was controlled by
enlarger optics)
34
IFS: Hybrid image slicer optical layout
2nd iteration
• Optical layout
35
Packaging Concepts
36
Dewar Based on MOSFIRE
• 1.4 m inside diameter
Top view
Bottom view
• Pink ring will not be present
37
Imager and Scale Changer in Dewar
• 1.4 m inside diameter required 6 fold mirrors
38
Larger Dewar
• 1.8 m inside diameter, 3 fold mirrors in imager path
39
IFS Optical Path
• Hybrid slicer, paraxial elements for camera and collimator
40
Responses to Review Comments
• Q: IFS scale changer, why two relays when OSIRIS uses 1?
A: OSIRIS lenslet pitch is 250 microns. Comparison of
magnifications:
SAMPLE
SCALE
10mas
OSIRIS
DAVINCI
66x
20mas
35mas
50mas
17.8x
10x
6.9x
19x
13.3x
Also, from the OSIRIS design note:
“The design fails to meet the wavefront error budget at the extreme
wavelength ranges in the two coarsest scales.”
41
Responses to Review Comments
• Question: Why add field flattener, when it increases distortion? Will it
introduce a color-dependent focal shift?
• Answer: The field flattener is not in the baseline design, but it will
extend the field over which the system is diffraction-limited, since
field curvature is the dominant source of wavefront error. It sits very
close to focus, so the color-dependent focus term is negligible.
42
Responses to Review Comments
• Question: Why such large OAP angles?
Answer: OAP1_DAVINCI has such a large off-axis angle because
OAP4 of the AO relay has a large off axis angle (41 degrees). In
order to obtain good pupil quality at the cold stop, OAP4_relay and
OAP1_DAVINCI have similar opening angles. The angle on
OAP1_DAVINCI produced the best quality at the pupil plane.
Because OAP1_DAVINCI has a large opening angle,
OAP2_DAVINCI must also be large to minimize aberrations in
relaying the image.
43
Responses to Review Comments
• Question: Why a 25 mm cold stop mask?
Answer: This size mask was considered a good choice to allow
fabrication of a precision mask matched the Keck telescope pupil
and central obscuration using either wire EDM or photo-chemical
processes
44
Responses to Review Comments
• Question: Why are the filters after the cold stop?
Answer: There appeared to be more space available after the cold
stop. Certainly if there are advantages to the filters being before the
cold stop there is adequate space for a filter wheel there.
45
Responses to Review Comments
•
Peter’s 6.4.6.1:
– The coronagraph requirements came from Table 4 in version 2.2_v6 of
the NGAO Science Case Requirements Document.
– Ok for 3". Only static aberrations will change.
– Wavelengths are easily changed. J and H are close to the correct
values, the value for K is the short wavelength cut-off. DAVINCI
photometric band CWLs are: K 2.2 microns, H 1.635 microns, J 1.25
microns.
– 170 nm rms wavefront error was chosen as a median value based on
previous NGAO performance budget estimates.
– Median seeing (also from Jim Lyke). I will take 0.56" in future
simulations.
• Peter’s 6.4.6.3: We will make this comparison.
• Peter’s 6.4.6.4: For H we can use 90% of the aperture so it’s not as
big of a deal. See next page for a graph of H band sensitivity.
46
Sensitivity in H band
SNR
Integration time in s
47