From relder@space.mit.edu Thu Jan 30 15:49:47 1997
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Date: Thu, 30 Jan 97 15:49:13 EST
From: relder@space.mit.edu (Dick Elder)
To: dd@space.mit.edu, mm@space.mit.edu, kaf@space.mit.edu
Subject: mis-aligned gratings
Status: R

Using poly monitor HA 2032 I measured the apparent roll angle created when the 
film is inserted in the alignment beam between the PEM and the gold grating 
bars. This polyimide monitor was chosen because it seemed to be stretched in one 
direction during mounting.   

I tested with grating ME1404 because it showed little polyimide effect, MD1300 
and  ME1401 because they shifted relatively large amounts in one direction and 
ME1414 because it shifted some in the opposite direction.  In all cases, H2032 
created a peak shift of 1.5 arc minutes.  The poly film behaves like a grating 
with four nulls and peaks as it is rotated through 360 degrees which would 
explain why only some gratings were affected.  

Pushing on the frame to increase or decrease the film stress causes the offset 
to increase and decrease.  The film has no effect when inserted into the beam 
between the grating and the detector.

The only M polyimide monitor available appears to be stress free and causes no 
offset when inserted into the beam.

Jane has the poly wafer from lot 7.  Let me know if you want it tested.

Dick