Introductory remarks by Bob Thicksten, Bob Brucato, and Mark Klaene

Paul Giordano: Optical Maintenance
	Paranal Techniques (Paul Giordano)

[PG viewgraphs here "Optical Maintenance of the VLT mirrors in
2001-Present Situation and Future Developments" Part A, and "Coating
and Cleaning"  Part B]

Q:  What is the white powder left after washing?
A:  Not known, suspect related to alcohol.
A:  May be dirt in the air absorbed by the liquids during the
washing.  Powder disappears when you clean in class 100 clean room.
A:  Alcohol is hydroscopic and absorbs stuff from the air.
Q:  How do you dry the mirrors?
A:  Air dry.
Q:  Is 3000 liters of DI water the only water used?
A:  No, tap water is used in the early steps.
Q:  What about using 99.95% CO2?-some people have problems.
A:  Not at Paranal.
Q:  How do you accomplish the calibration of reflectometer?
A:  By using reference mirror.
Q:  How do you remove white powder?
A:  Wipe with soft tissue.
Q:  What about the Zito filter for CO2 cleaning?
A:  Has been recently redesigned.  Doesn't work at 30 degrees F at
14,000 ft.  New redesign has tank heater.  Palomar has used cheap
micron filters with success.  Other people are using Coleman Grade 4,
99.99% pure.
Q:  Also, what about relative humidity limits?
Q:  With low humidity at Paranal, any trouble with static?
A:  No.
Q:  How do you measure dust?
A:  Met1 detectors at 20 and 30 meters.  Will add one inside
enclosures.  Use to determine opening/closing.  Also have filtered
air in dome Class 5000.
Q:  How does the dust monitor work?
A:  Scattered light in laser beam.
Q:  How does Keck deal with problems with static discharge and other problems?
A:  Use heaters, also eliminates icing which debrades aluminum.
Q:  How do you get grease on the mirror?
A:  Not only grease, but a lot of other things get on mirrors.
Q:  Does the mirror substrate change the regime of the chemicals you use?
A:  Yes.
Q:  Why use particular alcohols
A:  Isopropanols and ethanols tend to be cleaner.
Q:  Who made the chamber?
A:  Linde (sp?) and Debussey (sp?).
Q:  During sputtering, how long does it take to spin the mirror?
A:  About 20 minutes.
Q:  Doesn't one spin of sputtering leave an overlap, or empty band?
A:  A small one.
Q:  How long does entire coating process takes?
A:  About 1 week per primary mirror.
Q:  How much time lost for a washing?
A:  About a day.


  "Project for Protected Silver Coating"-Paul Giordano  [viewgraphs presented]

Q:  What is salt-fog "exposure"?
A:  Usually is test for durability of the coating.
Q:  What is coating thickness of overcoats, and do you need an undercoat?
A:  Don't know.
Q:  Do some Si overcoats have absorption problems in the IR?
A:  Not if you make them very very thin.
Q:  Why not use the silver on the smaller mirrors, leave alum on the primaries?
A:  Plan to start with the smaller mirrors, work to larger.
Q:  Problems with glow discharge?
A:  Too far from surface of mirror.
Q:  Does ultra-high vacuum improve reflectivity?
A:  answer not recorded.



Coating and Cleaning (Juerg Rey, and Maarten Blanken, ING)

[presentation of handling, coating of W. Herschel 4.2-meter primary]-
viewgraphs presented

Q:  Who manufactured your coating facility, how much did it cost?
A:  Balzer, a million pounds in 1983.
Q:  Is the mirror support in tank stationary or does it rotate?
A:  Stationary.
Q:  Do you pre-melt filaments?
A:  No, but sounds like an attractive idea.
A:  You can buy filaments with the aluminum premelted in them, from
Westinghouse
Q:  Only one ring of filaments?
A:  Yes.
Q:  Pump during glow discharge?
A:  Yes.
Q:  What is ring of LN2 inside tank for?
A:  Cold trap helps vacuum, a little.
Q:  How long between glow discharge and coating?
A:  20 minutes.
Q:  Do you fire sequentially or simultaneous?
A:  Simultaneously.
Q:  Backfill?
A:  Air, oxygen, argon all used.
Q:  Magnetron system for system ever developed?
A:  Tests were done for Gemini, samples were very good.


[Maartin Blanken presentation here]- viewgraphs presented.


Q:  What is final rinse, and how do you dry mirror?
A:  Alcohol, pressured air.
Q:  Does anybody use lanolin?
A:  Nobody but Palomar.
A:  Preferable to have "clean room" during coating preps, human
debris during handling can get on mirror before coating.


[Cleaning Techniques, Gary Poczulp]-get presented

Q:  Does CO2 cleaning just knock dust of mechanically, or is there a
chemical component of CO2 cleaning?
A:  Yes, but there is limited value of CO2 cleaning for removal of
hydrocarbons (some evidence reported from use in the semiconductor
industry).  The important thing is to get the dust or whatever off
the mirror before a hydration event (condensing humidity) causes
chemical reaction between the contaminants and the aluminum.
Q:  During drying, use Kim Wipes?
A:  Yes.
A:  Palomar uses chamois and drag-wipes.  Gary P., WIRO, and Lick
have all used pat-wipe, and drag-wipe.  Some observatories use dry
nitrogen blow, but this requires controlling humidity around mirror.
Q:  Can you cause water the sheet off the mirror without wiping?
A:  JT Williams is working on a design with the Italian astronomers
for such a system for LBT.
Q:  Air knife?
A:  Gemini uses one.
Q:  Is there a minimum humidity you can wash a mirror in?
A:  Not that anyone is aware of.
Q:  How do you clean ethylene glycol stains on mirrors?
A:  You have to clean them with soap/water, several times.  Have to
do it fast because it can etch the aluminum.
Q:
A:

[Mirror Maintenance ESO, Alain Gilliotte(sp?]- viewgraphs presented
Q:  Does anyone use peel-off techniques?
A:  Only for small optics, and when you have a lot of time to let
cure.  Opti-Clean seems to be used successfully.
Q:  At what humidity levels do you CO2 clean?
A:  Below 40%, use high-pressure; below 80%, use low-pressure; above
80%, don't clean
Q:  How frequently CO2 clean?
A:  Site dependent, use time plots of reflectivity and scatter to
determine best frequencies.
Q:  If you only measure the mirror every two weeks, how do you know
if you're keeping up?
A:  You really only need to measure every month, if you are following
a good cleaning  regime.
Q:  What do you do about the Cassegrain hole during washing, and what
is elevation of telescope?
A:  Use rubber tubes and tires blown up to seal, telescope pointed at horizon.
Q:  DI water in pressurized container?
A:  No, just pumped.
Q:  What temp is DI water?
A:  Room temp.
Q:  Is there a way to break up surface tension?
A:  None given.
Q:  Is there a waiting period after realuminization before CO2 cleaning?
A:  OK, if you wait at least a week.



[Cleaning and Coating at CTIO, Max Boccas]- viewgraphs presented

Q:  Do you use 50% HCl or 5% for washing?
A:  5%.  The value in the viewgraphs is a typo.
Q:  Does grounding mirror minimize static charge and help avoid dust
collecting on mirror?
A:  No, claimed at CTIO and APO.  Earlier test by Robert Brown at LPL
also inconclusive.
Q:  Do you see any difference in mirror coating maintenance related
to different substrate?
A:  No.
Q:  Are the Met1 counters the ones for the job?
A:  Yes and no.  The measure the wrong particle size, and they're
designed to be used in clean environments.  Some of the newer Met1
units may be better in both ways.


General Cleaning discussion:

Q:  Any interesting results in laser cleaning?
A:  Not considered any better than CO2 cleaning, and more dangerous/difficult.
Q:  How about differences in low- and high-pressure CO2 cleaning?
A:  Subaru did a study, and Gary Poczulp has a lot to say about it.
Pressure and orifice size tune the flake size and softness, said JT
Williams .
Q:  What tube modifications are useful?
A:  Enlarge tube, insulate it, this extends region of phase change
for ice and makes larger, softer crystals.


Measurement techniques-Mark Klaene DL
HET Techniques - Tony Distasio

Q:  What is diffuser for HET reflectometer?
A:  Custom opal glass, known to be a pretty good diffuser.
Q:  Do you monitor the output of the source?
A:  No, have tested light source stability independently to be good
for ~15 minutes.
Q:  Has Denton commented on process problems?
A:  Denton won't talk much about it, proprietary.
Q:  What kind of IR blockers for system?
A:  Has built-in IR blocker, specialized for photomic response function.
Q:  How repeatable and accurate is system?
A:  Repeatable to 2%, accuracy very good.
Q:  Do you test in darkness?
A:  Yes.
Q:  Thermal problems?
A:  Yes, need a fairly long warmup, 1 degree [F or C, ??] thermal
stability for long-term measurements.
Q:  Cost?
A:  Components about $5k, system as-built about $8k.

KPNO Measuring Techniques (Gary Poczulp)- viewgraphs presented

Q:  How long after coating before measurement?
A:  Right after comes out of chamber, which is overnight from when
the coating is applied.
Q:  What about contacting mirror when dirty with photometer?
A:  OK if you don't slide unit, clean o-ring before reusing.
Q:  Should compare data to true specular photometer?
A:  Good idea.
Q:  How much pressure on the photometer read head to glass?
A:  Just touch and "seat," just want to keep light out and establish
correct distance from read head to glass.
Q:  How much does Minolta cost?
A:  $12k new, $6k refurbished.
Q:  What about coating thickness measurement?
A:  "Micro map - merle interferometer"  (?)
Q:  Ideal coating thickness?
A:  Ideal is 900 - 1000 Å, less than 700 Å and more than 1200 Å is bad.
Q:  Is the curvature of the mirror bad for photometric readings
A:  Not a problem.

DMO 4-color Spectrometer (Daniel Malaise)-viewgraphs presented

A:  Cannot measure reflectivity with laser diode.  Polarization and
notches in interference filter cause spurious results.  Also, laser
fluctuates with temperature.
Q:  Price?
A:  $12k.

2nd day starts here

SOFIA Plans (Bill Brown)- viewgraphs presented

Q:  Considered in-situ aluminizing?
A:  Was considered, but aircraft design considerations nixed it.
Q:  How to handle stripping fluids with all the structures on mirror?
A:  Skirts and fluid handling "tires" will be employed.
Q:  Thickness monitoring and location?
A:  Quartz system, location TBD.
Q:  What is the differential vacuum level?
A:  High vacuum 10-6, low vacuum at TBD, depending on outgassing.
Q:  Can you paint the structures for reduction of outgassing?
A:  Not without changing important emissivity characteristics.
Q:  Is there a seal at the edge of mirror in the tank?
A:  Considered dangerous to have a large differential pressure
front-to-back on mirror.


Subaru coating (Saeko Hayashi)- viewgraphs presented

Q:  Can you use the TMA microscan on uncoated class to get
cleanliness indication?
A:  Yes, TMA uses differential specular/scattered measurement, so you
only lose signal-to-noise when measuring uncoated glass.
Q:  How long does it take to load the filaments?
A:  Several hours.
Q:  What grade and how much CO2?
A:  Coleman 99.99, 4 tanks per cleaning.
Q:  Had any problems with condensation, or ice?
A:  None so far.
Q:  What is the angle that CO2 hits the mirror?
A:  At an angle like this [shows hand angle of about 45 degrees].
Q:  How is 2ndary silver coating done?
A:  With a chromium undercoat.  Has lasted 2 years with only a little tarnish.
Q:  How long does CO2 cleaning take?
A:  About 10 minutes.
Q:  Are there missed areas between nozzles?
A:  Maybe, could explain scatter in data from TMA.
Q:  What was being measured with hand-held unit during cleaning?
A:  CO2 levels, for safety.
Q:  How long do you fire the filaments, by groups?
A:  About 3 - 5 minutes for the whole cycle.
Q:  What was deposition technique for silver?
A:  Tantalum filaments.
Q:  What about glow discharge?
A:  Argon backfill at .1 Torr.
Q:  How much pressure rise during a firing?
A:  About a factor of 10.
Q:  How cold does mirror get after cleaning?
A:  Minus 2 degree C from ambient.


[Good splinter topic:  Safety for humans when large gas dumps are
used during cleaning, coating-how to monitor and protect.]

Gemini Washing and stripping (Chas Cavedoni)- viewgraphs presented

Q:  What direction for air-knife?
A:  Radial.
Q:  Do you experience faint scratches from calcium carbonate scrub?
A:  Don't know, could be a problem because not in a cleanroom environment.
Q:  Nitric acid vs. HCl?
A:  Nitric cleans better, but may damage glass.
Q:  What is distance from air-knife to class?
A:  Ranges from 4 to 18 inches.
Q:  Is there EPA concern about copper ions from Green River in effluent?
A:  Not known.
Q:  Soap used?
A:  Orvus.

Sputtering, Gemini Update (Clayton Ah Hee)- viewgraphs presented

Q:  Distance magnetron to glass?
A:  45 mm.
Q:  Who made the chamber?
A:  PSI.
Q:  How long do the rings take to coat?
A:  2 hours total.
Q:  Does sputtering need high vacuum?
A:  Not, except to keep things clean.
Q:  What pressure do you do the sputtering at?
A:  3.5 x 10 minus 3.
Q:  Can you do witness slides?
A:  Trying to figure where to put them to get representative samples.

Cleaning techniques for Aluminizing (Gary Poczulp)- viewgraphs presented

Q:  Does anyone use high-pressure water sprayer for mirror washing/stripping?
A:  Nobody seems to have any experience, except UA Mirror Lab uses HP
sprayer for cleaning out cavities of mirror cells from the back side.
Q:  Why do you push hard on the chalk scrub?
A:  Tests show that being aggressive doesn't change glass microroughness.
Q:  Do you do glow-discharge?
A:  Not anymore, seems to leave haze.
Q:  Do you adhesion test?
A:  Not regularly.
A:  Palomar finds that adhesion is poorer without glow discharge.
Q:  Does anyone look at scratches immediately after coating?
A:  Palomar and NSO monitor scratches by photos, maps.
Q:  Water temperature?
A:  Room ambient, e.g., 55 degrees F at Gemini
Q:  How do you do final rinse?
A:  Chug it right out of the bottle.
Q:  Humidity?
A:  During drying, if humidity low can use extra person to keep mirror wet.
Q:  Why use Texwipe TechniCloth TX609?
A:  It works OK, but there is a new Texwipe wiper that we're going to try.
Q:  Is there correlation between friction and cleanliness?
A:  If you feel friction, it's not clean.
Q:  Is anyone using UV lamps to detect contaminants?
A:  Doesn't seem to work better than visible light.
Q:  Can you use de-ionizing to protect clean mirror from static dust
collection?
A:  Works better on smaller optics.  CO2 snow better for larger.
Q:  How do you keep CO2 from contaminating glass?
A:  Use high-pressure, small pellets.
Q:  Works for all kinds of glass?
A:  Yes.
A:  MMT and Steward also use aggressive scrubbing.


Problems and solutions in washing, stripping and coating (Gustavo
Arriagad)- viewgraphs presented.

Q:  Did you pump or pour the DI water?
A:  First poured, next time will pump.
Q:  Why did you use DI water to rinse the Ca carbonate?
A:  Didn't get clean enough with the tap water-heater was inadequate.

Haze - and "unpleasant things stepped on in the dark" (Hal Petrie)-
viewgraphs presented

Q:  Nodularization of Al is the source of haze?
A:  Possible.
Q:  What is purity of aluminum?
A:  Was using 99.99, now using 99.999.  Didn't seem to make much difference.

Melt-in of filaments (Bob Thicksten)- viewgraphs presented

Q:  If you don't squeeze the alum. loop on tight, does the transition
curve change?
A:  Yes, the initial phases are slowed down, can take several minutes
instead of tens of seconds.
Q:  How long does it take to pre-coat filaments?
A:  About 2 days.
Q:  What is the amount of Al per filament?
A:  .035 gram per filament, for 200-inch telescope.
Q:  What is deposition rate of coating?
A:  Hard to answer, since filaments are fired individually.
Q:  How about baffles to limit angles of deposition?
A:  Need extreme angles to get uniform coating thickness.
A:  KPNO added shrouds to limit spread to 59 degrees.
Q:  Why does the pressure go up when you flash the aluminum?
A:  It can't be the aluminum, because the ion gauge works on
nitrogen, etc.  Maybe it's hydrogen?

Keck coating problems (Tim Saloga)- viewgraphs, video presented

Q:  How big is tank?
A:  105 inches.
Q:  Where to you ground CO2 wand?
A:  Bottom of cherry picker.
Q:  Why choose 1100 A for coating thickness?
A:  Pinholes, optical density, uniformity OK.

3rd day Discussions

Mailer:  Gary Rosenbaum put out proposal for optics mailer.  Some
wanted to keep discussions on TOG group, about a dozen wanted to
subscribe.  Decided to keep it on TOG, to subscribe send mail to
Chuck Claver  at noao.  Need to consider web-based subscription
mechanism, an archive retrieval capability, and a posting bulletin
board function.  These could be added to existing TOG mailer, or in a
new mail facility.  Need to talk to Chuck about this.
cclaver@noao.edu, tog@noao.edu.  Also, group wants to distribute
e-mail address of this meeting to the attendees.

Future meeting:  Silver coatings, blue-enhanced coatings, and
addition of new people to group suggest frequency of every 2 years.
This was generally agreed-to by the group.  Also, useful to post
aluminizing schedule on TOG so people could schedule visits to watch
coatings.  SPIE and Opto-southwest meetings also could be venue for
our discussions.  People seem to prefer the more informal setting.
Next meeting in 2003.  Location could be Palomar, Hawaii, or Chile.
Organizing committee to include Bob Thicksten, Alain Gilliotte, Gary
Poczulp, Mark Klaene.

Special coatings:

Issues and contacts:  strip-ability, polarization, thickness
uniformity, SiO with pinholes can be stripped, Denton, QSP, Newport
thin films lab (did SAO coating), NOAO can do overcoats up to 16
inches.  Lick can do overcoats up to 144 inches.

Alain Gilliotte talked about measure complete efficiency of
telescope.  Need non-contacting, daytime instrument, portable.  Needs
to be sensitive in the blue (310 or 350 nm), and need to measure
emissivity in IR.  ESO has tried to get throughput measures through
the telescope using standard stars, but is largely unsuccessful
because of variations in extinction effects.  Dan Malaise showed a
design of a two-detector throughput instrument that measures daytime
sky through the telescope and compares it to a direct optics-less
measurement.  Some discussion of whether portable instruments can
really be useful compared to on-sky telescope measurements, due to
narrow-angle scattering.  Seems like there's a place for both
instruments that measure individual instruments, plus on-sky tests.
APO is planning to do an on-sky throughput monitoring program, will
be reported on TOG.  Alain Gilliotte, Mike DiVittorio, Paul Giordano,
and Bruce Gillespie offered to be on a committee to define
requirements (wish list) for reflectivity, scattering, and emissivity
testing devices.

Metrology:  Company in Fla. Called Ocean Optics?  Anybody familiar
with their spectrophotometer-something maybe to look at.

Witness samples-no discussion.

CO2 cleaning equipment-Can test CO2 cleanliness by filling beaker,
put clean glass lid sample on top, invert and let CO2 sublimate
overnight and check the sample.  Zito filter is 0.5 micron, needs to
have tank heated to get enough pressure which is still barely usable.
Keck has had trouble 99.95 CO2 for cleanliness.  Also tanks without
dip tubes leave 10% in tank, but may avoid contaminants in bottom of
tanks.   Need a small hand-held CO2 system?  Zito and Va-tran make
them.

Palomar vents tanks with 99.99 Oxygen to "harden" and build the AlO
layer as quickly as possible to prevent other contaminants and the
help protect the surface by toughening it.  The evenness of the oxide
layer is important to UV reflectivity, can't wait too long to build
it.

Can use CO2 to dust off telescope light baffles, but doesn't work
well where surfaces are rough or really dirty.

Glow discharge recipe?  Not really, highly variable techniques.  See
Holland's book.

--

Mark Klaene
Observatory Engineer, Deputy Site Manager		voice: 505 437 6822
Apache Point Observatory				fax:   505 434 5555
PO box 59
2001 Apache Point Rd
Sunspot NM 88349