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DAVINCI Mini-review

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

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DAVINCI Mini-review

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  1. DAVINCI Mini-review Sean Adkins, Renate Kupke, Sergey Panteleev, Mike Pollard and Sandrine Thomas April 19, 2010

  2. 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

  3. 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

  4. 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

  5. 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

  6. Approach to design/build to cost • Ensure that the instrument capabilities are well matched to key science requirements • Ensure that the instrument capabilities are matched to the AO system in order to maximize the science gains • Understand which requirements drive cost • Resist the temptation to add features • Maximize heritage from previous instruments • Evaluate ways to break the normal visible/near-IR paradigm of using different detectors in separate instruments

  7. NGAO Parameter Space

  8. 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

  9. Summary of Capabilities

  10. The DAVINCI Concept • Imager with on-axis IFS mode • FOV • Coronagraph • Sky background limited performance

  11. Imager Sensitivity Zero points and background magnitudes for DAVINCI imaging DAVINCI imaging sensitivity

  12. IFS Sensitivity

  13. DAVINCI 13

  14. 14

  15. Imager 15

  16. Quality of Pupil Image at cold stop 16

  17. Quality of Pupil Image at cold stop 17

  18. Imager 18

  19. Imager Transmission 19

  20. Scale changer magnification requirements Lenslet pitch at IFS image plane is 1.2 mm. This compares to 250μ pitch of the OSIRIS lenslets. 20

  21. IFS Scale Changer 21

  22. Scale changer, JHK 22

  23. Scale changer, IZ 23

  24. 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. 24

  25. 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

  26. 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

  27. 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

  28. IFS: Hybrid Image Slicer Optical Layout • Pupil plane conversion to virtual slit plane. • Central line symmetry • Enlarger optics between lenslet and field splitting mirrors

  29. 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

  30. Full field pupil images at detector Curvature of 40 sample long sub-slit image 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

  31. 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

  32. IFS Spectral Format • Distribution of spectra at detector (example)

  33. 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

  34. 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)

  35. IFS: Hybrid image slicer optical layout 2nd iteration • Optical layout

  36. Packaging Concepts

  37. Dewar Based on MOSFIRE • 1.4 m inside diameter • Pink ring will not be present Top view Bottom view

  38. Imager and Scale Changer in Dewar • 1.4 m inside diameter required 6 fold mirrors

  39. Larger Dewar • 1.8 m inside diameter, 3 fold mirrors in imager path

  40. IFS Optical Path • Hybrid slicer, paraxial elements for camera and collimator

  41. 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: 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

  42. 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

  43. 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

  44. 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

  45. 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

  46. 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

  47. Sensitivity in H band SNR Integration time in s 47

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