PFI on theThirty Meter Telescope Snapshot of Concept Study

1
PFI on theThirty Meter TelescopeSnapshot of
Concept Study

• LLNL/UCSC, JPL, U. Montreal

Extreme AO system (16,000 actuators)
High speed (few Khz update) High contrast coronag
raph (Vis Nulling Intef) Post Coronagraph wavefro
nt sensor (like GPI) Imaging spectrometer One pu
rpose of study impact of Telescope Design
2
TMT Reference Design and Program

• Telescope Architecture
• 30m filled aperture, highly segmented (800)
  telescope
  
• Wavelength coverage 0.31 28 µm
• Both seeing-limited and adaptive optics observing
  modes
  
• AO system requirements and architecture defined
• First generation instrument requirements defined
• TMT Schedule (High Level)
• Design and Development Phase (DDP) (2004
  2008)
  
• Includes Feasibility Study RFP
• Construction Phase (2009 2014)
• Early Operations Phase (2012 2016)
• Operations Phase (2016 2024)
• High-level science objectives (PFI)
• 1. Systematic studies of the extrasolar planet
  population in the solar neighborhood
  
• 2. Imaging very young planets (0 15 Myr) in the
  process of forming or migrating 100 pc distances
  
  
• 3. High-SNR studies of planetary atmospheres and
  their astrophysics
  
• 4. The studies of circumstellar disks ranging
  from young protoplanetary disks through debris
  disks to high-density extrasolar zodiacal debris
  in inner solar systems.

3
Goals of Study

• We want to make sure that the telescope design
  does not fundamentally limit the achievable
  contrast
  
• Long exposure requirement after speckle
  suppression is 10-8
  
• (goal of 10-9) from 3 to 64 l/D (34 to 725
  milliarcsecs)
  
• This implies an instantaneous contrast of 2 x
  10-7 (goal of 2 x 10-8)

4
Wave-Optics Simulation

• Telescope Pupil (Fortran or Matlab)
• 4 mm gaps would require 32K X 32K pixel FFTs
  ?use Gray Pixel approximation to generate pupils
  
• Also generated exact central obscuration and
  supports
  
• 1K x 1K active pupils (30mm/pixel)
• Phase error added in pupil plane
• AO System (Uses ARROYO)
• Wavelength1.65 um, mono-chromatic
• Spatially filtered Shack-Hartmann WFS with 32x32
  pixels per subaperture
  
• 127 x 127 Actuator DM with a least-squares
  reconstructor
  
• Iterate until converged
• Diffraction Suppression (Matlab)
• Lyot Coronagraph Radial Sinc2
• Two stage Nuller with 3.12 meter shears

5
System Layout
Nulling Coronagraph
Beamsplitter
Phase
-
Shifting
Mirror
Beamsplitter
C
C
D
Sampling
Beamsplitter
Beamsplitter
S
c
i
e
n
c
e

• q4 nulling interferometer
• Post coronagraph WFS and PSF estimator (Cal
  system) _at_ science l

C

• Extreme AO system
• Pyramid WFS (vis)
• Woofer/Tweeter DMs
• 10K20K actuators
• Few Khz update

Imaging Spectrometer
a
m
e
r
a
S
c
i
e
A
n
r
c
r
a
e
y

• Contrast limitations
• Telescope/AO residual aberrations (quasi static
  speckles)
  
• Atmospheric speckles
• 1 sec speckle lifetime in dark hole
• Removal of atmospheric speckles by PSF calib.

PSF subtraction Spectral (Methane band) Coheren
ce (Cal WFS)
6
Segmentation and Obscuration of Pupil

• 738 Segments
• Segments are 0.6 m on a side
• 4 mm gaps
• Central obscuration 3.65 m circle
• 3-50 cm compression supports
• 6-10 mm support cables

7
Contrast from Segmentation and Obscuration of
Pupil

• Nuller exceeds contrast goals at all field angles

8
Nuller

• Architecture Two-stage linear pupil shear
  nulling interferometer
  
• Simulation paradigm
• Contrast performance linear sin4 transmittance
  coronagraph
  
• End-to-end 3 pupil copies with shear, phase
  shift, and amplitude weighting

Transmittance for Two-Stage Nuller with
Shear 3 Hex Segment Widths (3.12 m)
Lyot Stop for Two-Stage Nuller
9
Contrast From Segment Reflectivity Variations

• TMT pupil with 1 segment reflectivity

10
Segment AberrationsBefore and After AO

• RMS 9.1 nm
• P-V 199 nm

• RMS 17.3 nm
• P-V 242 nm

11
Wavefront Error Table
12
Telescope Aberrations Summary

• Telescope (without PSF subtraction/calibration)
  optics is being specified to not limit the
  coronagraph _at_ 10-8 _at_ 3l/D and beyond. IWA
  25mas _at_1.2UM
• Amplitude control for segment reflectivity
  variations may be needed to meet this.
  
• Two approaches for PSF subtraction goal 13x10-9
• Spectral (target must have a strong spectral
  signature, ie the methane band in exo-planet)
  
• Coherence (post coronagraph wfs estimate PSF
  based on coherence of starlight)
  

13

• If the known planets were at 20pc, an IWA of
  25mas
  
• A contrast of 10-8 to 10-9, would set this as a
  limit