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News Highlights

Keck Adaptive Optics

The adaptive optics (AO) systems on Keck I and Keck II deliver diffraction-limited image quality in the near-infrared, using either natural guide stars (NGS) or a combination of natural and laser guide stars (LGS). While the two AO systems are similar, their design and performance have diverged with the development of the Keck All-Sky Precision AO (KAPA) upgrade on Keck I and the High Order Advanced Keck AO (HAKA) upgrade on Keck II.

Keck I: KAPA AO System

Deformable Mirror: 349 actuator Xinetics
High-Order Wavefront Sensor: 20x20 subaperture Shack-Hartmann operating at up to 2000 Hz.
Natural Guide Star AO: Uses a single NGS with R<15 within 30 arcsec of the science target. Note: Image quality will be better in LTAO mode for R>12.
Laser Tomography AO: Uses 4 LGS on a 15.2 arcsec radius square asterism to provide improved image quality with high sky coverage. Tip-tilt measurement can be provided either by a STRAP unit in the optical (NGS R<18) or the TRICK sensor in the near-infrared (NGS K<15) using NGS within 60 arcsec of the science target.
Science Instruments: OSIRIS
Performance: NGSAO, KAPA LTAO

Keck II: HAKA AO System

Deformable Mirror: 2844 actuator ALPAO
High-Order Wavefront Sensor: 57x57 or 29x29 subaperture Shack-Hartmann operating at up to 2000 Hz.
Natural Guide Star AO: Uses a single NGS with R<15 within 30 arcsec of the science target. Number of spatial modes controlled depends on guide star magnitude. Note: Image quality will be better in LGSAO mode for R>13.
Laser Guide Star AO: Uses a single laser guide star to provide high-order AO correction. Tip-tilt measurement is provided by a STRAP unit in the optical using NGS R<18 within 60 arcsec of the science target.
Science Instruments: NIRC2, SCALES (arriving in 2026), HISPEC (arriving in 2027)
Tech Demo Instruments: ORKID, Zernike WFS, CRED2
Predicted performance: K (2.20µm), H (1.63µm), J (1.25µm)

Additional features are available to AO observers:

Fast & Furious: The Fast and Furious algorithm can be used to optimize image quality in NGSAO mode, correcting for variable non-common path aberrations and WFS centroid gain errors. The correction is a function of pupil angle, and thus F&F is most useful when in Vertical Angle mode.
AO Telemetry: The AO systems save full frame rate WFS and DM telemetry to a server, which is then extracted into .npz files corresponding to each science image. These telemetry files can be provided to interested observers.


Keck I optical bench layout.	Keck II optical bench layout, including the future HISPEC fiber injection unit and IWA infrared pyramid wavefront sensor.