parabolising questions

Started by triumphst, 11/24/2014 07:39PM
Posted 11/24/2014 07:39PM Opening Post
what are the effects of the back side of the uncoated mirror in star testing. Does it create an additional reflection?
Posted 11/24/2014 10:35PM #1
No problem from the back side.

Rolando
Posted 11/29/2014 02:36AM #2
Posted 04/28/2015 01:59AM #3
I think the responders didn't quite catch what you said here. The LASER COLLIMATOR would indeed give a faux return from a specular back side. We experience that sort of thing all the time when doing pre-alignments of the Spatial filters for Interferometry in Aerospace applications. And some of those mirrors are SO precise (front AND back) that an in-process uncoated optic will give one or more false signatures. One easy trick is to just wet or even breathe on the back side...then its false signature will be the one to momentarily disappear. Nother trick is to put peelable "strip-coat" on the back, which elims it's faux return. yet another (that we used in production on thousands of parts) get giant sheets of High Contrast Sterolith Film, expose to light, process to opaque black, wet in soapy water and adhere it to the back of an in-process test mirror. The wet gelatin index matches AND adheres to the back, rendering it absentee for short duration of the test. Peel off and use on the next part. A few such films will last a whole shift (hundreds of tests). Use another the next shift. We tested tens of thousands of mirrors this way and it greatly reduced cost. We had previously been spray painting the backs black for testing and then stripping the paint later before coming up with that! The Test Set was of course fully-automated for so many parts, so we couldn't screw around too much or take too long. Like I said - your responders seem to have missed your comment regarding the "laser collimator." Anyone reading this---if you want a REAL challenge...ponder trying to align and then USE a multi-arm white-light interferometer! The coherence length is fractional wave over arms that are feet (or miles) long! PS - we STILL haven't detected Gravity Waves...sigh! Tom Dey – optomanic Tom

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