Short question, what are they (diffraction gratings) and what are they used for? Dave was so kind to include some with the laser he sold me, but apart from a groovy effect they produce when looking through them at a candle or even better, a TV, what do they do? When I shine a laserbeam at them, they produce a couple of copies of that beam, in a 3 by 3 pattern.
The holowiki is rather empty about the gratings and other HOE's:
http://holowiki.com/index.php/Holograph ... l_Elements
And speaking of that laser, on the lasertube, a 1145p, there is a marking indicating the plane of polarisation. It is indicated by an arrow, but it is pointing along the tube itself, something like this:
I would have expected an up/down arrow, but what does this tell me about the plane of polarisation?