[ATM] What can I do with this mirror?

[Paul A. Valleli]

John,
This mirror is not the one I was thinking of. I left
AOCC four months before it was completed and the
Visidyne System was very similar but made at Optical
Systems & Technology, Inc, of Billerica MA., which
was a spin-off of Diffraction Limited of Bedford,
MA.
Bill Brady had also worked at Itek and was my
replacement. Bill married the boss's daughter!
The test setup was as I thought, as it is one of the
best ways to test very steep mirrors.
We had a 24-inch Collimator that was built for the
Voyager Project and it had a series of illuminated
pinholes. The outgoing light was captured by the
mirror under test and relayed to the side of the
optical bench with a Newtonian diagonal. The image
spot was simply scanned with a knife edge and the
transverse motion measured from the first hint of a
shadow to total extinction of the Foucault Pattern.
Quick and Dirty, but inexpensive.
The 0.13mm would have been measured with a
micrometer.
Note that the zonal irregularity is only guessed to
be <500 A, or about 1/10th wave over a small zone
width - probably  1/2 to 1 inch.
The Knife Edge test can detect errors of 1/60th
wave, provided the source is only a few times larger
than the diffraction limited blur and bright enough
to be observed.

This is what makes it a subjective test - with a
wide slit - say 0.010 to 0.020", a rough, zony
mirror can look smooth, but the rms is large and the
Strehl Criterion low.
Paul

---- Original message ----

  Date: Mon, 09 Jan 2012 11:03:23 -0800
  From: John Sutter <jds-ml at sutters.com>
  Subject: Re: [ATM] What can I do with this mirror?
  To: "Paul A. Valleli" <valleli at rcn.com>
  Cc: atm at atmlist.net
  >That's quite the coincidence. Not what I was
  hoping to hear, but>there are always
  possibilities. Worst case, I guess it could end up
  as>a part of a Burning Man project.>>I put up the
  scanned paperwork I have on it at:>
  http://www.sutters.com/ATM_Stuff/20120108_mirror_docs.pdf>>It's
  good to know it's not beryllium as
  well.>>Thanks,>>-- John>>On 1/8/2012 8:43 PM, Paul
  A. Valleli wrote:>> BOY ! are you lucky, John,>> I
  was the project manager and optical test engineer
  for this 24-inch>> Cass. System and you provided
  just enough info for me to uniquely>> identify
  it.>> It was made of 6061-T6 Aluminium Alloy and
  thermally stabilized for very>> high altitude use,
  with liquid nitrogen and oven baking cycles.>> The
  customer was Visidyne Corp. a private contractor
  to the USAF at>> Hanscom AFB in Bedford MA. They
  sub-contracted the optics to Sylvania. I>> can't
  tell you what it was used for but it was basically
  a light bucket>> to feed infrared light to an IR
  spectrometer.
  >> In 1976, opticians did not know how to polish
  bare aluminum - it is>> technically far different
  from pitch-polishing glass. The process>>
  procedure was to machine the aluminum forging
  close to shape, anneal the>> material, and then
  progressive machine to final dimensions. after
  the>> first set of thermal cycles, we apply a very
  thin layer of electroless>> Nickel - a substance
  which does not have a crystalline structure - it
  is>> amorphous, just like glass, but the polishing
  is done with pitch and>> sub-micron sized aluminum
  oxide ( basically Sapphire).>> After collimation
  testing to the parabolic figure, the mirror was>>
  electroplated with pure Gold for 99% reflectance
  from the red to thermal>> infrared wavelengths.
  Plated Gold is much more durable than vacuum>>
  coated Gold.>> I believe the spec. was for a blur
  circle less than 0.13 mm or 130 microns.>> I am
  afraid for your sake, that that is about ten times
  the blur spot of>> a visual scope and is very far
  from diffraction limited - hence the>>
  'light-bucket' designation. Modern IR detectors
  have around 30 micron>> pixels, but it is likely
  in those days, that they used a single pixel of>>
  MerCadTel, cooled to minus327F.>> I left AOCC in
  the Fall of 1976 and they moved the operations
  to>> Sarasota, FL in about 1980.That was a year
  after we made six similar>> telescopes for the
  Mariner Jupiter/Saturn/Uranus/Neptune "Grand
  Tour",>> now known as the JPL Voyager Program. The
  primaries were 20-inch>> diameter Nickel Plated
  Beryllium primaries at F/0.8 ! - and>>
  hyperboloidal secondaries.>> The rest is history,
  two of the spacefraft are at the edge of the
  Solar>> System, travelling a BILLION miles every
  three years.>> What to do with the mirror ? You
  could strip the Gold if you are>> comfortable
  about working with Potassium Cyanide but the
  underlying>> Nickel only has a reflectivity of
  55%.>> How about a cigarette lighter?>> Starman
  Paul>>>> ---- Original message ---->>>>>> *Date:*
  Sun, 08 Jan 2012 01:53:41 -0800>> *From:* John
  Sutter <jds-ml at sutters.com>>> *Subject:* [ATM]
  What can I do with this mirror?>> *To:*
  atm at atmlist.net>> >I picked up a 24" mirror at
  auction a few years ago.>It was made>> in 1976. I
  have a little>documentation on it, but few of the
  figures>> mean>much to me.>>Details:> Diameter:
  24.4"> Clear Aperture: 24">>> Centering Accuracy:
  w/in 0.050 (no units, assuming ")> Final Focal>>
  Length: 35.5"> Vertex Radius of Curvature: 71">
  Shape of figured>> surface: Parabaloid> Surface
  accuracy: <= 500 A> Diameter of circle>> of least
  confusion: 80-100% w/in 0.13 (no units, >assuming
  ")>>> Surface finish: 80/50>>There is a 4" hole in
  the center.>Coating is>> gold.>>There is a hand
  drawn diagram of the test setup, but it>>
  doesn't>really seem to convey much information
  about the mirror>> itself.>>There is an note about
  thermal cycling as part of a test:>>> Thermal
  Cycle> Liquid Nitrogen to +350 F> 3 times> 1)
  Incoming> 2)>> Post nickel plate> 3) Before gold
  plate>>It was made by Applied>> Optics Center Corp
  in Burlington! , MA for GTE>>
  >Sylvania.>>_______________________________________________>ATM>>
  mailing list http://www.atmlist.net/>>>>