On-sky performance during verification and commissioning of the Gemini Planet Imager's adaptive optics system

TL;DR

This paper reports on the on-sky performance of the Gemini Planet Imager's adaptive optics system, highlighting its new technologies like Fourier-based wavefront reconstruction, modal gain optimization, and LQG controllers, during verification and commissioning.

Contribution

It demonstrates the successful implementation and operation of innovative AO technologies on-sky, including wavefront reconstruction, modal gain optimization, and vibration suppression.

Findings

Efficient wavefront reconstruction and gain optimization are functioning as intended.

LQG controllers effectively suppress vibrations.

Spatial filter reduces aliases but is often oversized for stability.

Abstract

The Gemini Planet Imager instrument's adaptive optics (AO) subsystem was designed specifically to facilitate high-contrast imaging. It features several new technologies, including computationally efficient wavefront reconstruction with the Fourier transform, modal gain optimization every 8 seconds, and the spatially filtered wavefront sensor. It also uses a Linear-Quadratic-Gaussian (LQG) controller (aka Kalman filter) for both pointing and focus. We present on-sky performance results from verification and commissioning runs from December 2013 through May 2014. The efficient reconstruction and modal gain optimization are working as designed. The LQG controllers effectively notch out vibrations. The spatial filter can remove aliases, but we typically use it oversized by about 60% due to stability problems.