NIR LOWFS for Keck and TMT

Roger Smith & David Hale

ComparisonKeck IR TT TMT IRIS OIWFS

Detector 2.5 µm H2RG 2.5 µm H2RG Subarray, Low noise

Acquisition FoV 1200 x 1200 1000 x 1000 pixels

Plate scale 0.100 0.002 arcsec/pixel

Acquisition FoV 120 ~5 arcsec

Passband K J+H

Optics Full field, reimager with cold Lyot stop

3 probe arms with 2x2 lenslet inserted on brightest star.

Output frame rate (minimum)

1000 80 Hz

# windows,size

1 to few. 2x2 to 4x4

1 or 4,4x4 nested in 14x14?

Topics• Thermo-mechanical– For Keck: proposal (optical layout, dewar layout)– For TMT: eDrawing

• Detectors considered• H2RG read mode• Resulting noise vs frame size (or rate)– For TMT– For Keck

• TMT sky coverage• Bad pixels: noisy, hot or insensitive

Keck 1 Layout

LGS AO control schematic with the new NIR TTS system added (upper right). A fold located just in front of the science camera reflects light to the NIR TTS assembly mounted on a focus stage. The TTS output is processed to provide TT control of the Tip-Tilt Mirror (TTM) as an alternative to the existing visible TTS (STRAP) or in combination. Focus information, if available, could be used to control the wavefront sensor (WFS) focus.

Keck 1 Pickoff Options

Keck 1 reimaging dewar

TMT: 3 R-theta probes

1 of 3 sensor dewars

Sensor Dewar

Focal planeGetter on cold head

Cryotiger, decoupled from detector

Cold filter location

Preliminary Cooling Curve

Masses and surface areas are guesses, to be updated from solid model !

Ample power margin; safe cooling rate.

Keck 1 noise vs frame rate