PFI on theThirty Meter Telescope Snapshot of Concept Study

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PFI on theThirty Meter Telescope Snapshot of Concept Study

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High contrast coronagraph (Vis Nulling Intef) Post Coronagraph wavefront ... Woofer/Tweeter DM's. 10K~20K actuators. Few Khz update. q4 nulling interferometer ... – PowerPoint PPT presentation

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Title: 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

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)