Speaker
Abstract content <br>(Max 300 words)<br><a href="http://indico.saip.org.za/getFile.py/access?resId=0&materialId=2&confId=28" target="_blank">Special Chars</a>
Generation of speckle using scattering that is spatially incoherent is a
common, and often annoying, phenomenon but has not been as yet utilized in
adaptive optics for wavefront sensing. This paper describes a method whereby
light is scattered from a surface (which may be a plane within a sample
being imaged) and then an image is obtained of the speckle created at two
defocused planes at some equal but opposite distance from that pupil. Due to
the correlation of speckle with propagation, a cross correlation of detected
intensity (or amplitude, via interferometric detection) can be used to
measure the wavefront gradient. The key advantages of this technique include
the ability to alter the sensitivity of the wavefront gradient signal vs.
the spatial sampling of the wavefront gradient. A further extension
demonstrates how multiple but distinct regions of scattering can be utilized
to produce overlapping but mutually uncorrelated speckle. The individual
speckle cross-correlation can then be extracted to result in a set of
wavefront gradients that, in astronomy, would be described as star-oriented.
Astronomical data-reduction approaches can then be used to produce a
tomographic or 3D wavefront solution. In this case, the wavefront sensor
hardware is no different to the single-scattering source case and the
angular source selection is done by computation rather than multiple
devices; thus costs and complexity are minimized at the expense of detection
and computational time.
