Cascina 26 Aug 2008 Weekly Meeting1 Viewport cleaning & inspection Procedure and Results Richard Day EGO optics group R. Maillet N. Menzione C. Bradaschia.

Cascina 26 Aug 2008 Weekly Meeting 1

Viewport cleaning & inspectionProcedure and Results

Richard DayEGO optics group

R. MailletN. Menzione

C. BradaschiaE. Genin


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.


Outline

Present test bench created and steps in procedure.

Report on Larson viewport quality and selection process.

Further actions to be taken.


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.


Procedure

Bench installed by Nicola & Rodolphe in the “locale lavagio”


Engraving & frame cleaning

Each viewport engraved with an “EGO” reference number

UXX = UncoatedHXX = Antireflection coating for HeNeYXX = Antireflection coating for YAG


Engraving & frame cleaning

Grease and loose particles cleaned from metal frame

“knife” inspected for vacuum compatibility


Cleaning of optical surface

Blow off loose dust and particles with clean air


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.


Inspection of optical surface

Fiber illuminator reveals those stains not seen by conventional light sources



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



Take photos of most serious damage

Glass Scratches




Glass marks




Glass bubbles



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


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



Stress higher at edgesStress direction parallel to the edge of glass



Same viewport turned by 45 degrees


Packing window

Remove dust

Place in cover

Wrap in cellophane


Update database

Temporary location has been created:

http://wwwcascina.virgo.infn.it/optics/viewport_inspection

See Franco’s demonstration of definitive database


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.


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.

Cascina 26 Aug 2008 Weekly Meeting1 Viewport cleaning & inspection Procedure and Results Richard Day EGO optics group R. Maillet N. Menzione C. Bradaschia.

Documents

glassweekly meetingcascina

geninweekly meetingcascina

yagweekly meetingcascina

inspection process

cleaning of optical

clean airweekly meetingcascina

key codeweekly meetingcascina

wet optical tissue