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"
Monday, August 28, 2006
OCT
Low coherence interferometry (LCI), low coherence reflectometry, optical coherence tomography (OCT) or partial coherence reflectometry all refer to the same basic set-up, an interferometer under low coherence illumination. A variety of LCI systems have been researched and applied to different fields, in measuring electric or magnetic field, pressure, acceleration, flows, etc. One of the most exciting application of LCI is OCT for imaging tissue. This has revolutionised the imaging technology of superficial tissue, images from retina with less than 5 microns have been recently reported.
Low-Coherence Interferometry is a powerful tool to "section" a transparent object. The technique is currently evolving quickly with applications in medicine in general and ophthalmology in particular. The OCT technology is non-invasive and provides high depth resolution, therefore the technology was applied to different types of tissue, skin, hair, burns, etc. Visualisation of cells, microorganisms, hair, brain and the interior of arteries have been reported with depth and transversal resolution of 5-15 microns. OCT has also been used to image integrated circuits, characterise fibre Bragg gratings and optical waveguides and in surface analysis. In combination with confocal microscopy, OCT can in principle offer 1 micron resolution along all three axes. The OCT field requires an interdisciplinary approach.
The AOG in Kent is at the forefront of OCT system development. The group has pioneered the en-face OCT technology, the first dual channel confocal-OCT instrument for the eye, multi-interferometer configuration to collect simultaneously images from different depths and produced 3D OCT visualisation in real time.
Low-Coherence Interferometry is a powerful tool to "section" a transparent object. The technique is currently evolving quickly with applications in medicine in general and ophthalmology in particular. The OCT technology is non-invasive and provides high depth resolution, therefore the technology was applied to different types of tissue, skin, hair, burns, etc. Visualisation of cells, microorganisms, hair, brain and the interior of arteries have been reported with depth and transversal resolution of 5-15 microns. OCT has also been used to image integrated circuits, characterise fibre Bragg gratings and optical waveguides and in surface analysis. In combination with confocal microscopy, OCT can in principle offer 1 micron resolution along all three axes. The OCT field requires an interdisciplinary approach.
The AOG in Kent is at the forefront of OCT system development. The group has pioneered the en-face OCT technology, the first dual channel confocal-OCT instrument for the eye, multi-interferometer configuration to collect simultaneously images from different depths and produced 3D OCT visualisation in real time.
Wavefront - Wikipedia, the free encyclopedia
Wavefront - Wikipedia, the free encyclopedia: "Wavefront
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For the notion of wave front in functional analysis, see wave front set.
In optics, a wavefront is the locus (a line or surface in an electromagnetic wave) of points having the same phase. Since optical frequencies are so high, the temporal component of optical waves is ignored, and it is only the phase of the spatial oscillation that is described. Additionally, most optical systems and detectors are indifferent to polarization, so this property of the wave is also usually ignored.
Contents [hide]
1 Simple wavefronts and propagation
2 Wavefront aberrations
3 Wavefront sensor
4 See also
5 External links
[edit]Simple wavefronts and propagation
Strictly speaking, all optical systems can be described with Maxwell's Equations. However, given the above simplifications, Huygens' principle provides a quick method to predict the propagation of a wavefront through, for example, free space. The construction is as follows: Let every point on the wavefront be considered a new point source. By calculating the total effect from every point source, the resulting field at new points can be computed. Sophisticated computational algorithms are often based on this approach. Specific cases for simple wavefronts can be computed directly. For example, a spherical wavefront will remain spherical as the energy of the wave is carried away equally in all directions. Such directions of energy flow, which are always perpendicular to the wavefront, are called rays.
The simplest form of a wavefront is the plane wave, which when propagating can be seen to give rise to new plane wavefronts, as the corresponding rays are parallel to each other. Technically, this is referred to as a coll"
From Wikipedia, the free encyclopedia
Jump to: navigation, search
For the notion of wave front in functional analysis, see wave front set.
In optics, a wavefront is the locus (a line or surface in an electromagnetic wave) of points having the same phase. Since optical frequencies are so high, the temporal component of optical waves is ignored, and it is only the phase of the spatial oscillation that is described. Additionally, most optical systems and detectors are indifferent to polarization, so this property of the wave is also usually ignored.
Contents [hide]
1 Simple wavefronts and propagation
2 Wavefront aberrations
3 Wavefront sensor
4 See also
5 External links
[edit]Simple wavefronts and propagation
Strictly speaking, all optical systems can be described with Maxwell's Equations. However, given the above simplifications, Huygens' principle provides a quick method to predict the propagation of a wavefront through, for example, free space. The construction is as follows: Let every point on the wavefront be considered a new point source. By calculating the total effect from every point source, the resulting field at new points can be computed. Sophisticated computational algorithms are often based on this approach. Specific cases for simple wavefronts can be computed directly. For example, a spherical wavefront will remain spherical as the energy of the wave is carried away equally in all directions. Such directions of energy flow, which are always perpendicular to the wavefront, are called rays.
The simplest form of a wavefront is the plane wave, which when propagating can be seen to give rise to new plane wavefronts, as the corresponding rays are parallel to each other. Technically, this is referred to as a coll"
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