[ATM] Induced astig experiment or how to torture a mirror.

[Dale Eason <atmpob@yahoo.com>]

Tonight I tried a little experiment using my 16 x 1
inch mirror and my interferometer to measure how much
astig can be induced by self weight on the test stand.
 I tilted the mirror back 20 degrees then put a small
piece of foam behind the top edge to support the back.
 The lateral support was only one point on the bottom
edge.  This would be like supporting the mirror by
only two points on its back close to the edge.  This
caused it to sag between the two points.  The surface
PV error was 1 wave!.  RMS wavefront error was 1.3
waves.  When supported correctly in the cell this
mirror measures about 1/5 wave astig on the wavefront.

If someone can figure out how to model this condition
in PLOP we can see if it compares. 

Dale Eason

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