Thursday, October 6, 2011

The science and art of optical contacting

  John Wallace
  Senior Editor
  Laser Focus World
First, the science (I'll go through this quickly, because I want to get to the art). Optical contacting is a method of adhering two pieces of polished glass together without using cement. It takes advantage of very short-range molecular attraction; as a result, the two cleaned surfaces have to have exactly the same shape down to a couple of nanometers. Usually, both surfaces are flat, but can in certain instances be convex/concave. Because the surfaces are in contact, their glass/air interfaces essentially disappear and there is no Fresnel reflection whatsoever. Optical contacting is an excellent way of assembling certain ultraprecise optical components and systems, and has other uses in the optical shop as well.

Back when I was an optical engineer, I worked with some very talented optical technicians who made this technique seem easy. Then for fun I tried it -- and could never get it right. I saw splotches of rainbow colors, which were interference fringes where the surfaces did not bond; I saw little circular reflective areas where some specks of dust remained, preventing the contacting from happening. NASA should be very happy that I'm not on their team.

Art that needs excellent scratch/dig specs
Now, on to the art. I recently visited LightMachinery (Nepean, Ontario), which, along with excimer and CO2 lasers, makes precision optics. As I was leaving, Vaz, one of the company's optical technicians, handed me a document, which I looked at later in the day. As it turns out, Vaz Zastera is an expert at optical contacting, not only for LightMachinery but for his own art too.

For his optically contacted art, he works in collaboration with another artist named Jiri Harcuba. Jiri will do an engraving on an ultraflat piece of glass that Vaz has made; Vaz then optically contacts the piece to another flat, creating a larger glass object within which the engraving floats. Vaz also creates optically contacted art pieces that are unengraved.

Optically contacted three-layer sandwich; engravings in each layer inside by Jiri Harcuba. Cold work by Vaz. (Courtesy of Vaz Zastera)

Optical contacting technique was used to assemble "Dove." Eight dove prisms are optically contacted to a big right-angle prism. (Courtesy of Vaz Zastera)

And now for some science: This is an optical assembly for a first-of-its-kind instrument for Boston University and NASA. It is called a Monolithic Achromatic Nulling Interference Coronagraph (MANIC). It will be used in a telescope system to block (null) out suns when observing exoplanets (planets orbiting a star other than our Sun). It is all optically contacted. (Courtesy of Vaz Zastera)

By the way, Vaz's site says, "Optical contacting can be easily learned with practice." Hah. Maybe if you’re not a fumblefingers like me.

For more on Vaz's art, see:

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