Cascina 26 Aug 2008 Weekly Meeting 1
Viewport cleaning & inspectionProcedure and Results
Richard DayEGO optics group
R. MailletN. Menzione
C. BradaschiaE. Genin
Cascina 26 Aug 2008 Weekly Meeting 2
Motivation
80 new viewports to be installed in the ITF.
Each viewport needs to be cleaned and inspected before installation.
Create database containing state of viewports at time of installation.
Test bench and procedure required in order maximize efficiency and quality of cleaning and inspection process.
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Outline
Present test bench created and steps in procedure.
Report on Larson viewport quality and selection process.
Further actions to be taken.
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Procedure
1. Engraving and frame cleaning.
2. Vacuum compatibility inspection.
3. Cleaning of optical surface.
4. Inspection of optical surface.
5. Polariscope inspection.
6. Packing Window.
7. Update database.
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Procedure
Bench installed by Nicola & Rodolphe in the “locale lavagio”
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Engraving & frame cleaning
Each viewport engraved with an “EGO” reference number
UXX = UncoatedHXX = Antireflection coating for HeNeYXX = Antireflection coating for YAG
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Engraving & frame cleaning
Grease and loose particles cleaned from metal frame
“knife” inspected for vacuum compatibility
Cascina 26 Aug 2008 Weekly Meeting 8
Cleaning of optical surface
Blow off loose dust and particles with clean air
Cascina 26 Aug 2008 Weekly Meeting 9
Cleaning of optical surface
The bigger the optical the surface the harder it is to clean without leaving alcohol stains
Revolutionary technique using turntable.Drag “wet” optical tissue from the center to the outer rim.
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Inspection of optical surface
Fiber illuminator reveals those stains not seen by conventional light sources
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Inspection of optical surface
What are we looking for?
• “micro-scratches”
• Glass Scratches
• Glass Pits
• Glass Mark
• Glass Bubble
• Glass chipping
• Coating scratches (coated windows only):
• Coating mark (coated windows only
In red indicates a potential vacuum risk
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Inspection of optical surface
Take photos of most serious damage
Glass Scratches
Cascina 26 Aug 2008 Weekly Meeting 13
Inspection of optical surface
Take photos of most serious damage
Glass marks
Cascina 26 Aug 2008 Weekly Meeting 14
Inspection of optical surface
Take photos of most serious damage
Glass bubbles
Cascina 26 Aug 2008 Weekly Meeting 15
Inspection of optical surface
Difficult to have an overview of window damage just from photos
Make a map of all the damage for each side with a key code
Cascina 26 Aug 2008 Weekly Meeting 16
Polariscope inspection
Viewport placed between two crossed polarizers.If glass is stressed it becomes birefringent.We see light where there is stress
Small areas with high stress can indicate defects in glass
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Polariscope inspection
Stress higher at edgesStress direction parallel to the edge of glass
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Polariscope inspection
Same viewport turned by 45 degrees
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Packing window
Remove dust
Place in cover
Wrap in cellophane
Cascina 26 Aug 2008 Weekly Meeting 20
Update database
Temporary location has been created:
http://wwwcascina.virgo.infn.it/optics/viewport_inspection
See Franco’s demonstration of definitive database
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Results
All 20 uncoated Larson viewports have been cleaned and inspected
Vacuum inspection: No problems
Optical inspection:•Viewports arrive relatively dirty•Many viewports have light scratches•>10% have glass bubbles at the edge•Almost all viewports have glass marks often near the center
→ Maybe dirt baked onto surface•10% have non-uniform interface between glass and rim
However: inspection of existing viewports reveals similar defects.
Polariscope inspection: No areas of high stress observed
Conclusion•Optical quality is not good.•Almost all viewports do not show signs of having a vacuum risk.
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Work to follow
•Contact Larson to see how they can improve their handling procedures
•Introduce selection process. For every 10 viewports:
•Choose 3 best → to be used in areas where good optical quality needed.
•Choose 3 worst → to be used areas where we don’t care.
•Any viewports that seem non-conform and could have a vacuum risk are put
aside for closer inspection of destructive testing
•Due to viewports being very dirty on arrival, review cleaning procedures to
minimize risk of scratching during cleaning.
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