REPORT FROM DAVID VAUGHNN:
July 18, 2000

  G. Jacoby and I visited the 4mPFC this AM to inspect the quality
  of the sol-gel A/R coating on the internal surface of the last
  element (#4A) and installation of the new Baffle Ring.  Here is
  a summary of our findings and recommendations:

CONCLUSIONS & RECOMMENDATIONS:

  1. The questionable surface is likely non problematic.  Proceed
     with scheduled redeployment and checkout.

  2. The Baffle Ring is likely to significantly reduce (but not 100%
     eliminate) the magnitude of the reported stray light anomaly.
     Add additional black RTV to the interface between the Baffle
     Ring and rear surface of the 4mPFC to close up the gap.

FINDINGS:

  Figure works only with fixed width fonts:

            |---|   |---|   |---|       RISLEYS
            |#1 |   |#2 |   |#3 |       |-||-|       
            |A B|   |A B|   |A B|       | || |       |---|
            |   |   |   |   |   |       | || |       |#4 |
            |   |   |   |   |   |       | || |       |A B|
    FRONT   |   |   |   |   |   |       | || |       |   |  REAR
            |   |   |   |   |   |       | || |       |   |
    --->    |   |   |   |   |   |       | || |       |   |  <---
    F->R    |   |   |   |   |   |       | || |       |---|  R->F
            |   |   |   |   |   |       |-||-|       ^   ^
            |---|   |---|   |---|                    |   |-- BAFFLE
                                                     |
                                                     |-- SOL-GEL

  1. The 4mPFC was mounted horizontally in its cradle in the Main
     Floor Plate Loading Room.  It was properly covered and in good
     general shape.  Using a drop light at the rear and viewing
     the reflection of the light from Surface 4A, we verified the
     characteristic reported by S. Andree 7/11/00 and documented by
     J. Glaspey:  http://claret/glaspey/KP/corrector.html

  2. When placing the drop light at the front and viewing the surface
     from the rear, we were not able to see the effect.  In fact,
     both this way and reversing the light and viewing position
     appeared to be very "clean".

  3. We did a close visual inspection of the effect/pattern.  The
     irregular hexagonal "lines" are actually composed of a string
     of small bubble like rings that look like evaporation spots.
     The hexagonal pattern is not in the 50 mm DIA center of the surface.
     The bubble/rings appear gradually at about 25 mm RAD from the
     center.  They are first randomly distributed and then at about
     a RAD of 50 mm the hexagonal string pattern starts to become
     evident.  The definition of the pattern increases with radius
     to the edge of the part.  The hexagonal cell size is 5 - 7 mm
     and the little bubble/rings have lateral dimensions of
     50 - 200 um.  There are approximately 5 bubble/rings along each
     side or "string" of an irregular hexagon.

  4. The light scattered from the bubble/rings (i.e., the pattern)
     is roughly the same magnitude as the wiping/cleaning residue
     on the rear (4B) surface.

  5. A laser pointer was aimed both Front-to-Back (F->B) and B->F
     in the dark.  The intensities of the spots formed at each
     air-to-glass interface were viewed from both ends (forward and
     back scattering).  The two external surfaces produce the brightest
     spots (most scattering).  Surface 4A (the sol-gel surface) was
     not substantially different than the other internal surfaces
     (George believes the spot intensity was noticeably less).
     As the beam was moved spatially over the surfaces, they would
     "twinkle" as scattering centers became illuminated/avoided.
     When the laser was entering from the rear and Surface 4A was
     viewed from the the rear, it appeared that the twinkling was
     related to the bubble/rings.  The magnitude of the "twinkling"
     was less than the external surfaces, though possibly brighter
     than the other internal surfaces.

  6. I believe that the pattern is innate, a result of the application
     of the sol-gel which was done on a spinning table.  Whether or
     not it has always been there (and never observed) or has appeared
     since deployment (brought on by either age or exposure to dry
     N2) I do not know.  I do not believe the pattern will get worse.
     However, it would be prudent to recheck it in a year.  George
     took additional photographs of the surface.

  7. The laser was aimed from the front to the internal cylindrical
     surface of the #4 Axial Preload Ring.  This is the surface which
     we believe causes the stray light anomaly.  The new Baffle Ring
     appears to block the deleterious scattering.  It was viewed from
     both sides.  A non inconsequential amount of light "sneaked"
     through the approximate .1 mm gap between the OD of the baffle
     and the ID the Rear Cell.  S. Andree installed the baffle with
     four "tabs" of RTV about 25 mm in arc length EA.