DAVINCI Mini-review

Sean Adkins, Renate Kupke, Sergey Panteleev, Mike Pollard and Sandrine Thomas

April 19, 2010

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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

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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– 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

– 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

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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

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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

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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

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NGAO Parameter Space

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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

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Teledyne min. spec. for substrate removed H2RG

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Summary of Capabilities

Capability Integral Field Spectrograph Imager Wavelength Coverage

I, Z, Y, J, H, K (0.7 to 2.4 µm) I, Z, Y, J, H, K (0.7 to 2.4 µm)

Filters 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

Spectral Resolution ~4000 1 FOV ~ 4" x 4" with 50 mas sampling

~ 1" x 1" with 10 mas sampling ≥ 15"

Spatial 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

≤ λ/2D, possibility of multiple pixel scales

Throughput (instrument only)

~40% (goal) > 75% (goal, without coronagraph)

Detector 4096 x 4096 (Hawaii-4RG) 4096 x 4096 (Hawaii-4RG) Detector Performance

Background limited Background limited or detector limited depending on observing band

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The DAVINCI Concept

• Imager with on-axis IFS mode• FOV• Coronagraph

• Sky background limited performance

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Imager Sensitivity

Photometric Passband

Cut-on, nm

Cut-off, nm

CWL, nm Zero point Background, mag./sq. arcsecond

I band photometric 700 853 776.5 27.42 22.13 Z band photometric 818 922 870 27.24 21.28 Y band photometric 970 1070 1020 26.97 17.28 J band photometric 1170 1330 1250 27.05 16.04 H band photometric 1490 1780 1635 27.07 13.76 K band photometric 2030 2370 2200 26.52 14.78

Zero points and background magnitudes for DAVINCI imaging

Photometric Passband

Ave. Strehl (170 nm wavefront error)

Time per exposure

5 mag.

Time for single exposure to background limit, mag. = 27

I band photometric 15% 120 s 27.8 6.7 h Z band photometric 22% 120 s 27.9 5.6 h Y band photometric 33% 900 s 28.0 1800 s J band photometric 39% 900 s 27.4 560 s H band photometric 59% 900 s 26.5 70 s K band photometric 79% 900 s 26.7 280 s

DAVINCI imaging sensitivity

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IFS Sensitivity

Passband Cut-on, nm

Cut-off, nm

CWL, nm Zero point Background, mag./sq. arcsecond

I band spectroscopic 700 853 776.5 26.48 22.13 Z band spectroscopic 855 1050 952.5 26.90 20.68 Y band spectroscopic 970 1120 1045 26.49 17.05 J band spectroscopic 1100 1400 1250 26.89 16.33 H band spectroscopic 1475 1825 1650 26.40 13.79 K band spectroscopic 2000 2400 2200 25.85 14.62

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DAVINCI

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Imager

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Quality of Pupil Image at cold stop

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Quality of Pupil Image at cold stop

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Imager

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Imager Transmission

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Scale changer magnification requirements

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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

– 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.

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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.

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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– 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– 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

4x

40x40 40x40

40x40 40x40

40x1x10

8x800

80x80

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IFS: Hybrid Image Slicer Optical Layout

• Pupil plane conversion to virtual slit plane.– Central line symmetry

– Enlarger optics between lenslet and field splitting mirrors

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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

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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

Full field pupil images at detector

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Curvature of 40 sample long sub-slit image

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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)

– 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

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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)

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1Z2Z3Z4Z5Z6Z7Z8Z1Y2Y3Y5Y6Y7Y9Y4Y1J2J3J4J5J6J7J8J1H2H3H4H5H6H7H8H1K2K3K4K5K6K7K8K1I2I3I4I5I6I7I8Ileftright

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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

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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)

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IFS: Hybrid image slicer optical layout 2nd iteration

• Optical layout

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Packaging Concepts

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Dewar Based on MOSFIRE

• 1.4 m inside diameter

• Pink ring will not be present

Top view Bottom view

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Imager and Scale Changer in Dewar

• 1.4 m inside diameter required 6 fold mirrors

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Larger Dewar

• 1.8 m inside diameter, 3 fold mirrors in imager path

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IFS Optical Path

• Hybrid slicer, paraxial elements for camera and collimator

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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 20mas 35mas 50mas

OSIRIS 17.8x 10x 6.9x

DAVINCI 66x 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.”

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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.

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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.

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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

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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.

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• 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.

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Responses to Review Comments

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Sensitivity in H band

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SNR

Integration time in s