The AO system for the GTC-an update

Nicholas Devaney, Dolores Bello, Bruno Femenía, Alejandro Villegas, Javier Castro

Grantecan, Instituto de Astrofísica de Canarias

Marcos Reyes, Jesús Jimenez

Instituto de Astrofísica de Canarias

Preaching to the converted....(I hope!)

Log scaling to show PSF structure due to segmentation. Integration will smooth this structure to ~Airy rings as pupil rotates

GTC AO specifications

Correction in the near IR 1.0-2.5 m (goal: 0.8-5 m)

On-axis Strehl ratio > 0.75 at 2.2 m when r0=20cm at 0.5 m (bright guide star)

SR > 0.1 a 2.2 m for guide star mR>14.5

Corrected field = 1 arcminute (goal 2 arcmin)

Range of zenith angles 0-60

Transmission to science focus > 70% (1.0 < < 2.5 m)

Emissivity < 20% a =3.8 m

Seeing stats at GTC site

Cumulative histogram of seeing at the GTC site as measured using DIMM measurements; see http://www.iac.es/proyect/sitesting/site.html for more information.

Bright star Strehl ratio

K H J

r0=20cmZ=0

0.76 0.60 0.43

r0=15cmZ=0

0.69 0.50 0.32

r0=15cmZ=45

0.58 0.36 0.18

AO system outline

Whole system mounted on a fixed bench at Nasmyth. Optical derotation of image.

Deformable mirror has 21 actuators across the pupil (11.309m=pupil+3% radius) 250-300 actuators in use

Tip-tilt correction carried out by GTC M2 residual corrected by deformable mirror

Shack-Hartmann wavefront sensor tip-tilt derived from Shack-Hartmann measure Designed to upgrade for use with Sodium Laser

Guide Star

AO system outline

GTCAO optical design

Corrector: optical de-rotator 2 off-axis parabolas 2 DMs conjugate to atmospheric layers at 0 and 8

km altitude Beamsplitter ADC in the science path

Wavefront Sensor field lens (maintains pupil distance) collimator camera ADC included

Optics design - Correction system

deformablemirror (pupil)fold mirror

(8km)

OAP1

OAP2

ADCdichroic

Optical design of WFS

Field lens

ADC

Lenslet array

camera

collimator

Mechanical design

Scientific Instrument

AO system

Wavefront sensor

Interface with AO Instrument

Output beam focal ratio same as GTC

Dichroic cut-off at 0.9 m

Distance of exit pupil from focus = 6680mm (goal was to leave at position GTC exit pupil)

Need to fix tolerance on output beam position and direction affects tolerances of AO alignment current values 6’’, 3mm

Non-common path errors will be measured using Phase Diversity; may affect focus range of AO Instrument (or detector). Will probably be measured by moving the wavefront sensor

Mechanical design

Scientific Instrument

Optics bench

AO system

Imagerotator

Comments on comments....

Keep loop closed while nodding main problem is repeatability: Jitter of 0.004 arcsec corresponds to SR=0.96 at

2.2 m. In the image plane, this is 3.3 microns !!!!

IR WFS good in regions of high obscuration otherwise less sensitive (higher read noise and

background) best to have both IR and vis.

Upgrade path...

The first upgrade should be install a sodium laser guide star for single-conjugate operation This will provide good sky-coverage and allow

more science

Development of suitable sold state lasers is on-going (LLNL, CTI, Lightwaves, ESO...). Considering to contribute to development costs now.

There should be a parallel development of MCAO wavefront sensing.

The PDR

Dates fixed July 26-28

Three external reviewers confirmed

Mechanical design not as advanced as would be expected for PDR. Control system not designed.

List of documents for PDR:

PDR Documents1 GTCAO System Specifications2 Requirements for the GTCAO Detector and Controllor3 Requirements for the GTCAO wavefront corrector and wavefront

sensor mechanisms4 Preliminary Requirements for the GTCAO deformable mirror5 Requirements for the GTCAO Calibration system6 DCI AO system-AO Instrument7 Alternatives for the Deformable Mirror8 Alternatives for Detector and Controllor9 Optical Design of the GTCAO system wavefront corrector10 Optical Design of the GTCAO system wavefront sensor11 Mechanical Design of the GTCAO wavefront corrector and

wavefront sensor12 GTCAO Control system Use Cases13 Preliminary Integration and Test plan14 Simulations to assess the GTCAO wavefront sensor CCD pixel size15 Laser Guide Star market survey16 MCAO Simulations report17 Processing of the GSCII Star Catalog18 Phase screen alternatives19 Non-common path error calibration

AO Common user Science Instrument

FRIDA collaboration just started Main contributors:

Optics: Mexico and U. of Florida Mechanics: Mexico and IAC Software and detector control: IAC

Preparing a conceptual design. Should be ready by October 2004

Initial discussions are focussing on an imager and IFU spectrograph Resolutions foreseen range from 500 to about

30000

People willing to contribute should contact Beto López (jal@astrosen.unam.mx)hb

Planning

2003 2004 2005 2006 2007Preliminary DesignPDRDetailed DesignCDRFabricationIntegration & TestInstalation GTC