In one of the courses I met the Hartmann-Shack sensor, but I want to extend the knowledge about it in order to understand whether it can be used in my research.
For which aims the the Hartmann-Shack sensor can be used? How does it work?
Links to relevant papers/documents are welcome.
shack-hartmann sensor (shs) are used for measure and capture wavefronts. especially in technical optics the shs measure the deformation of a wavefront the pass through an optical system (e.g. objectiv, eye piece, or simple lens). the deformation give some statements about the kind aberrations of the optical system. you can also use shs for measure the ability of a optical set-up which transform wavefronts, e.g. a plane wave in spherical. further applications: laser-beam-measurements or characterize, measuring of the modulations-transferfunction functions (mtf) of optical systems and use shs to correct wavefronts, e.g. in adaptive optics.in front of shs there are a micro-lens array, they focus very small different pieces of the hitting wavefront to one pixel of an pixel array behind the micro lens array. that gives posibility to measure crabwise diffenrent phase shifts in the wavefront. watch the paper.
bye
https://www.tu-ilmenau.de/fileadmin/public/regelungstechnik/Mitarbeiter/Prof_Johann_Reger/reger_TIM2014.pdf
Yes, that is the most common use. There is one additional way, but that is not very easy to use. With some knowledge of layer thicknesses, you can use the shs to calculate the refractive index of layers or even stacks of layers by. You need to measure the Wavefrond through a reference and the stack you want to measure and if there is some kind of gradient, you can measure the optical path length difference and with the wavelength the refracive index. Not a very precise method, but sometimes there is no other way to gain that information. Of ourse, on the other way around, if you know the index very well, maybe its possible to measure layer thickniss with this method, but again its not easy to use, since the shs only shows gradients.
Imaging a plane wave incident upon a single lens. This wave is focussed to a single point in the focal plane of the lens. If the plane wave changes direction then the focal point moves sideways. Here we can think of the position of the focal point as telling us about the direction of the wave.
Now consider a rectangular array of lenses. A single plane wave incident upon the lenslet array will produce a rectangular array of spots, with exactly the same spacing as the lenses themselves. Indeed if this array of spots is perfectly regular then this is a demonstration that the incoming light was indeed a perfect plane wave.
Now consider what happens with the incoming light is NOT a plane wave. At each lenslet the local wave direction is defined and a spot is produced. BUT because the local wave directions are different, the array of spots produced is no longer regular. The more the local tilt of the wave, the more the spot is moved sideways. Looking at all the spot directions allows one to reconstruct the overall shape of the incoming wavefront (the spatial resolution of this reconstruction matches spacing of the lenslet array).
One advantage of a Hartmann-Shack sensor is that it is not subject to the fringe ambiguity associated with interferometry. Consequently it is a good technique for measuring bad, multi wavelength scale aberrations. This is very useful for measuring the aberrations associated with a turbulent atmosphere.
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