# Presentation: 853330

## PFI on theThirty Meter TelescopeSnapshot of Concept Study

**LLNL/UCSC, JPL, U. Montreal**

**Extreme AO system (~16,000 actuators)**
**High speed (few Khz update)**
**High contrast coronagraph (Vis Nulling Intef)**
**Post Coronagraph wavefront sensor (like GPI)**
**Imaging spectrometer**
**One purpose of study: impact of Telescope Design**

## 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.

## 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 /D (34 to ~725 milliarcsecs)
- This implies an instantaneous contrast of 2 x 10-7 (goal of 2 x 10-8)

## 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)
- Wavelength:1.65 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

## System Layout

**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.**

**Extreme AO system**
**Pyramid WFS (vis)**
**Woofer/Tweeter DM’s**
**10K~20K actuators**
**Few Khz update**

******4**** nulling interferometer**
**Post coronagraph WFS and PSF estimator (Cal system) @ science ******

**Imaging Spectrometer**

**PSF subtraction **
**Spectral (Methane band)**
**Coherence (Cal WFS)**

- Nulling Coronagraph

- Phase

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- Shifting

- Mirror

- C

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- Beamsplitter

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- Sampling

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## 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

## Contrast from Segmentation and Obscuration of Pupil

- Nuller exceeds contrast goals at all field angles

## Nuller

**Architecture: Two-stage linear pupil shear nulling interferometer**
**Simulation paradigm**
**Contrast performance: linear sin****4**** 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**

## Contrast From Segment Reflectivity Variations

- TMT pupil with 1% segment reflectivity

**Contrast From Segment Reflectivity Variations**

## Segment AberrationsBefore and After AO

**Segment Aberrations****Before and After AO**

- RMS: 17.3 nm
- P-V: 242 nm

- RMS: 9.1 nm
- P-V: 199 nm

## Wavefront Error Table

## Telescope Aberrations Summary

- Telescope (without PSF subtraction/calibration) optics is being specified to not limit the coronagraph @ 10-8 @ 3/D and beyond.  _**IWA ~ 25mas @1.2UM**_
- Amplitude control for segment reflectivity variations may be needed to meet this.
- Two approaches for PSF subtraction goal 1~3x10-9
- 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)

## If the known planets were at 20pc, an IWA of 25mas

**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**