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3 Questions with Karl George Sr.

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Karl George Sr. and Karl George Jr. Courtesy of Karl George Jr.
December marks the 40-year anniversary of the completion of the Hubble Space Telescope’s primary mirror. The coating for the 94-in. component took a full year to develop but had to be applied in a matter of minutes. The deposition process was performed by a PerkinElmer team and went off nearly without a hitch … nearly.

Karl George Sr., who led PerkinElmer’s team of coatings technicians, would later form Quality Thin Films with his son, Karl George Jr.

George Sr. has accumulated almost 60 years of experience in optical coatings. Photonics Media spoke with him about his largest project, the evolution of optical coatings, and Edmund Optics’ acquisition of his company.


What were the most challenging aspects of coating the Hubble mirror?

The size of the telescope mirror made this an unprecedented project. It was nearly 8 ft in diameter and composed of $15 million worth of glass. To load a mirror of that size into a vacuum chamber to clean it involved a more detailed set of steps than anything my team was used to. Once we loaded the mirror, we pumped for a week to remove oxygen and water. To have all the necessary pieces of machinery operate correctly at that scale was a challenge unto itself. And they did not all work all the time.

The coating was made of pure aluminum (three-millionths of an inch thick), with a film of magnesium fluoride (one-millionth of an inch thick) to prevent the aluminum from oxidizing and the resulting loss of reflectivity. To coat the mirror, we used electron beam guns, positioned 90° apart, to each coat 25% of the mirror surface. The aluminum went on first, followed by the magnesium fluoride.

Once the coating process began, we couldn’t stop: The longer we waited, the more oxygen was exposed to the aluminum, which would cause the surface of the mirror to oxidize. You only have a few minutes to move from aluminum to magnesium fluoride.

After the aluminum was deposited, only three of the four guns that we needed for the magnesium fluoride coating were working. In that moment, I told my boss that we could perform the magnesium fluoride coating with only three guns, each covering 33%.

For a project of the Hubble’s magnitude, that was a decision with huge implications for how the coating would be performed. Before we had to make that change, the fourth gun fired as planned and we were able to do the coating.

What have been some of the most apparent growth areas and developments in optical coatings since you entered the field?

I started at PerkinElmer as a thin-film technician in 1962. A lot of our work involved thin-film material stress analysis, and the goal was to develop new materials — metals rather than oxides — with the highest damage thresholds and optical performance. Today, there is heightened focus on the cleanliness of the optics to enable quicker and more effective coating and more precise measurements. There is also more attention given to durability. There has been a shift from simply developing products, to refining them for target applications.

Broadband antireflective (BBAR) coatings were coatings we were working with in the 1970s and ’80s. Now, they are commonly used with lasers, laser crystals, optical lenses, windows, and even eyeglasses. Many advancements have made these coatings more durable. If you are going to coat a pair of glasses, for example, they are going to be dropped, rubbed, and scratched. Not only do they have to reduce reflectivity, but they also must be highly durable.

There has also been tremendous progress in laser crystal growth and polishing. New materials, improved purity, and tighter tolerances have enabled laser systems to reach previously unattainable levels of precision.

Different types of coatings have emerged as well. For infrared optics, diamond-like carbon (DLC) coatings are used to coat the exterior of windows made from materials like germanium or silicon, while a regular coating goes on the interior of the window. DLC coatings are extremely scratch-resistant and are great for optical systems that are to go into harsh environments.

Quality Thin Films was acquired by Edmund Optics this year. Does that feel like a fitting culmination to a successful career in optics?

It does not feel like a culmination. It does feel like the right thing to happen at this time. What I am most proud of is the transfer of knowledge. I know that I have contributed to the growth of our industry, especially through my son. To be able to transfer all that I have learned in 58 years is what matters most.

At PerkinElmer, my colleague, my son, and I would drive 50 minutes to and from where we lived in Danbury, Conn., to our offices in Norwalk. Every day. On those drives we would talk about optics. That is how Karl Jr. developed his love and knowledge for the field. That is the one quality we always say we need to see in members of our workforce: They need to love what they are doing.

I feel very fortunate for the growth of our business and the field. When I started, there were two coatings available: magnesium fluoride and metal coatings. BBAR coatings, laser line mirrors, and lithium triborate coatings are all things that we have helped introduce or expand. Our processes, like our ion-assisted deposition method, have helped this industry move in new directions with new capabilities. We are proud to be able to bring that knowledge to Edmund Optics.

December marks the 40-year anniversary of the completion of the Hubble Space Telescope’s 94-in. primary mirror. The coating for the component took a full year to develop but had to be applied in a matter of minutes. Courtesy of Karl George Jr.


December marks the 40-year anniversary of the completion of the Hubble Space Telescope’s 94-in. primary mirror. The coating for the component took a full year to develop but had to be applied in a matter of minutes. Courtesy of Karl George Jr.

Photonics Spectra
Sep 2021
3 Questions

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