[ATM] What can I do with this mirror?

[John Sutter]

After reading your write-up on Thomas, I'd feel bad doing anything
that might damage the mirror.  It seems like an artifact.  I'll keep it
as a novelty and use it for science demos at the local school.

Do you have recommendations for good demos for kids?  Kids love burning,
but probably not on school property around here.  Maybe a laser pointer
on a pivot at the focal point after talking about the properties of the
shape.

I'll add a copy of your write-up to the mirror's paperwork too.

Thanks for the great information,

-- John

On 1/9/2012 10:46 PM, Paul A. Valleli wrote:
> 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 fo! r 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/>>>>
>
>