IR Pyramid WFS

Near-infrared wavefront sensing is a critical enabling technology for science with AO on current and future telescopes. It will enable high contrast science of exoplanets and dust obscured regions, and high sky coverage for extragalactic science. It can be used to extend the performance of NGS AO to fainter targets and to increase the sky coverage of laser guide star (LGS) AO. Furthermore, it allows the application of optimal wavefront sensing approaches (e.g. pyramid and Zernike wavefront sensing) due to the AO correction at near-infrared wavelengths. All of the extremely large telescopes (ELTs) are planning to use infrared wavefront sensing as part of their AO facilities.

We will build an IR Pyramid wavefront sensor for the Keck II adaptive optics system, as part of a collaboration between W.M. Keck Observatory, the University of Hawaii, the Subaru telescope, and Caltech, leveraging the following developments:

The University of Hawaii (UH) has worked with Selex to develop and characterize the SAPHIRA infrared avalanche photo-diode (APD) arrays including implementing a traveling test camera. This camera has been demonstrated on-sky for imaging at the IRTF telescope, for tip-tilt sensing with the Robo-AO system (Baranec et al., 2015), and for speckle imaging with the Subaru SCExAO system. UH will be implementing faster readout electronics suitable for high order AO wavefront sensing. The proposed PWFS will be integrated with this camera.

The California Institute of Technology and W. M. Keck Observatory have implemented a Hawaii-2RG-based near-infrared tip-tilt sensor with the Keck I LGS AO system (Wizinowich et al., 2014). This system is being used for science and is transitioning to routine science operation. The system is also being used for additional technical demonstrations including higher order focal plane sensing (e.g. focus), optimal tip-tilt algorithms, and the use of multiple tip-tilt stars to reduce tip-tilt anisoplanatism.

Subaru has developed high sensitivity visible-wavelength wavefront sensors (i.e. non-linear curvature and non-modulated pyramid) to enable high contrast imaging on large telescopes. This experience will benefit the development of the proposed near-infrared PWFS through reuse of algorithms and control software. The UH SAPHIRA camera will be configured as a simple PWFS for preliminary experiments with the SCExAO system prior to the start of the proposed project (SCExAO will be unavailable for this purpose after June 2016).

© Dimitri Mawet 2017