Adaptive optics with an infrared Pyramid wavefront sensor

Abstract

Wavefront sensing in the infrared is highly desirable for the study of M-type stars and cool red objects, as they are sufficiently bright in the infrared to be used as the adaptive optics guide star. This aids in high contrast imaging, particularly for low mass stars where the star-to-planet brightness ratio is reduced. Here we discuss the combination of infrared detector technology with the highly sensitive Pyramid wavefront sensor (WFS) for a new generation of systems. Such sensors can extend the capabilities of current telescopes and meet the requirements for future instruments, such as those proposed for the giant segmented mirror telescopes.Here we introduce the infrared Pyramid WFS and discuss the advantages and challenges of this sensor. We present a new infrared Pyramid WFS for Keck, a key sub-system of the Keck Planet Imager and Characterizer (KPIC). The design, integration and testing is reported on, with a focus on the characterization of the SAPHIRA detector used to provide the H-band wavefront sensing. Initial results demonstrate a required effective read noise < 1e − at high gain.

Keck/NIRC2 L’-band Imaging of Jovian-mass Accreting Protoplanets around PDS 70

“…Using the 225 GHz radiometer measurements and the conversion from Dempsey et al (2013), we calculated that the average precipitable water vapor was 1.7mm. We used the infrared pyramid wave front sensor to control the Keck adaptive optics system as part of its science verification program (Bond et al 2018), rather than the facility Shack-Hartmann sensor. The pyramid wave front sensor operates at the H band, whereas the Shack-Hartmann operates at the R band, so it is better suited for redder stars such as PDS 70.…”

“…This paper reports on the results of L'-band imaging of the PDS 70 system with Keck/NIRC2 and the newly commissioned infrared pyramid wave front sensor (Bond et al 2018). In Section 2, we discuss the observations and the data reductions we performed to obtain astrometry and photometry of the two planets.…”

Reference Star Differential Imaging of Close-in Companions and Circumstellar Disks with the NIRC2 Vortex Coronagraph at the W. M. Keck Observatory

“…Additionally, wavefront errors due to the primary mirror must be sensed and corrected by the Shack-Hartmann wavefront sensor in the Keck AO system (Wizinowich et al 2000), but segment piston errors (or the "terrace" modes) are not seen by the wavefront sensor and are therefore not corrected. This issue may be mitigated by the pyramid wavefront sensor under development at Keck Observatory (Bond et al 2018).…”

Enabling discoveries: a review of 30 years of advanced technologies and instrumentation at the National Science Foundation

“…Keck AO has been supported by several ATI awards, including 1611623/Wizinowich, which supported the near IR pyramid wavefront sensor. 50 Advantages of pyramid wavefront sensing over the more common Shack-Hartmann method include greater sensitivity within the correction band and reduced susceptibility to aliasing. 51 The first pyramind wavefront sensor was demonstrated for the MMT telescope.…”

“…94,95 On-sky tests with a near-IR pyramid wavefront sensor and SAPHIRA device were recently accomplished at the Subaru SCExAO system using a camera supported by NSF 96 and on the Keck II telescope, as funded by a separate ATI investigation (1611623/Wizinowich). 50 Low read-noise, fast time response detectors will be crucial for pushing the limits in exoplanet studies. 97…”