Wavefront Sensor Overview

Wavefront Sensor Overview: "You are in: Telescope > Wavefront Sensor (WFS) Overview


Wavefront Sensor Overview

All observations with the Gemini telescopes require the use of wavefront sensors (WFSs) assigned to one or more stars to provide image motion compensation (fast guiding) and/or higher order correction. This is achieved by articulation of the secondary mirror, manipulation of the primary mirror figure (active optics, aO) and/or adaptive optics (AO). See an evaluation of the Galactic stellar surface density for expected WFS star availability.
Peripheral Wavefront Sensors (PWFS)
Two peripheral wavefront sensors are part of the Acquisition and Guidance (A&G) system located within the instrument support structure (ISS) cube. PWFS1 consists of a 6x6 lenslet array feeding 2D array detector and PWFS2 has a 2x2 lenslet array feeding its array detector. A selection of filters covering the optical and near-infrared (e.g., V,R,I) is available for each array. Mounted on rotary stages, and as their name implies, the PWFSs patrol an annulus of sky around the science field. The PWFSs are upstream of the science instruments and, whilst they may be moved into the centre of the field for engineering purposes, will vignette the science field unless positioned at sufficient distance. The minimum distance to avoid vignetting depends on the science field of the instrument.
The minimum angular distance (i.e. inner patrol radius) of the PWFS1 and PWFS2 stars from the field center differs for various instruments and their configurations. For example, the PWFS2 guide star must be at least the following distance off-axis to avoid vignetting the science field: NIRI imaging f/32 camera - ~4.2 arcmin; f/14 camera - ~4.6 arcmin; f/6 camera - ~5.0 arcmin; NIRI spectroscopy - depends on sli"