The Simple Life

From oemagazine August 2004
01 August 2004
By Rich Donnelly

My enthusiasm has always been for simplicity in everything I do," says Roland Shack, recipient of the 2004 Gold Medal of SPIE. Shack has pursued simplicity throughout his career as a way of making a difference in the lives of others.

Still a very active Professor Emeritus at the University of Arizona's Optical Sciences Center (OSC; Tucson, AZ), Shack says he still teaches "because that is what I love to do. This has ultimately been my real calling."

Shack sees the world of science as a playground requiring an educated innocence. He encourages students to be curious, "to understand what is happening before their eyes, and not take anything for granted. And do everything playfully, looking at the world with the spirit of a five-year-old, but making use of the knowledge they are accumulating in their education."

The simple advice he gives to students lives on, as John Greivenkamp attests. Shack is "one of the great figures in optics over the last half century," says Greivenkamp, formerly Shack's student and now his friend and colleague at the OSC.

"Much of the material I teach was derived from what Roland taught me," he says. "Bits of his class notes can still be found throughout my notes. I have certainly been infected by his enthusiasm, and I have no plans [for] being cured!"

Roland Shack (left) and Kurt Opperman at Perkin-Elmer, working on the Baker-Nunn Satellite Tracking Telescope in the fall of 1957 when Sputnik became the first satellite in orbit.

The two inventions that bear his name, the Shack-Hartmann test and the Shack cube interferometer, bear witness to his love of simple solutions.

"As you look at these two inventions you realize how simple, clever, and elegant they are," says Jim Wyant, OSC Director. "They are typical Roland Shack."

"I asked myself if satisfying my own curiosity was enough, or whether making a difference to somebody else was important."

The Shack-Hartmann test came about in an attempt to improve satellite images blurred by atmospheric turbulence. "Aden Meinel suggested that some of the light from the satellite could be siphoned off and put through a classical Hartmann screen so that the wavefront could be reconstructed, thus making image processing possible," says Shack. However, due to the low amount of light in satellite images, the massive amount of light lost in the Hartmann test is an issue. To improve the efficiency of the classical Hartmann test, Shack found that a small lens could be placed in each hole of the Hartmann screen to focus the light onto the photographic plate. It was then apparent that the screen was no longer necessary, and the lenses could be butted up against each other.

The Shack cube interferometer is used to test converging wavefronts at the center of curvature of a reflective surface. It combines a cube beamsplitter with a high-precision plano-convex lens. It is especially useful for its low cost (only one precision partthe plano-convex lensis needed) and its ability to produce a high-aperture lightcone for testing strongly curved wavefronts. For the unusual story behind the inspiration for the Shack cube interferometer, see Sidebar: The Genesis of the Shack-Hartmann Test and the Shack Cube Interferometer.

Shack's path to an educational career came by way of government and industrial research. "Most of the key moments were when I felt I didn't really fit in to what I was doing," he says. As a junior scientist at the National Bureau of Standards in the early 1950s, he pursued his interest in image formation and evaluation, and calls himself a "minor pioneer" in the development of the optical transfer function. But he didn't feel that people understood his work. "I asked myself if satisfying my own curiosity was enough, or whether making a difference to somebody else was important."

He moved to Perkin-Elmer (Norwalk, CT) where he quickly discovered his lack of interest in management, but "I could earn my keep in my engineering accomplishments," and help other engineers, he says. "In fact, helping others was what I did best, to my way of thinking."

A glass sculpture designed by Roland Shack. He has also worked in metalsmithing and jewelry making.

At Perkin-Elmer, Shack's mentor was Rod Scott, who persuaded him to pursue a PhD at Perkin-Elmer's expense. "He said it was embarrassing to admit to customers that I only had a BS in physics," Shack says. So he worked under Harold Hopkins at Imperial College (London, UK) and received his PhD.

Besides his technical creativity, Shack has had a lifelong interest in art, especially sculpture ("I think three-dimensionally," he says). He took a break from optics early in his career to obtain a BA in fine arts from the American University (Washington, DC). One of his works (see photo) was created as a retirement gift from the OSC to Jack Gaskill, "but it has become popular as a gift to subsequent retirees, including me." He hopes to find time in his busy retirement to devote more time to art.

Pam and Roland Shack in Monument Valley, AZ.

He met his wife, Pam, when they both worked with a Washington, DC, theater group, and they have four children (David, Karen, Diana, and Michael). "In growing up, not one of them had any interest in anything scientific. But they have all turned out to be fine people anyway, and I love them all dearly," he says.

The Gold Medal is not the first award Shack has received from SPIE. He also was honored with the A.E. Conrady Award in 1998. This year at the Annual Meeting in Denver, he and colleague Robert Shannon will be the subject of a special tribute conference on 4 and 5 August.

"I have always been impressed with his understanding of the fundamental principles behind image formation, system design, diffraction, and optical testing," says Shannon. "These ideas live on and expand through the careers of his students. His recognition by SPIE is well-deserved."

Jim Wyant recalls how he first heard of Shack: "Before I joined the OSC faculty I used to come to the university every February to interview students for the Itek Corporation. The students told me there was one professor at OSC who was a genius and his name was Roland Shack. Once I got to know Roland I realized the students were right. He seems to know everything in classical optics, and he always has a simple, elegant way of solving difficult problems."

Shack's influence at OSC even extends to how the center marks time, Wyant says. The early days of the center were "a little fuzzy," according to Wyant, but "we decided it must have started in 1964 because that was the year Roland Shack came to the University of Arizona. Roland has been so important to the Optical Sciences Center that we think it is very fitting to say that OSC started when Roland came here."

Shack and Jack

By Jack Gaskill

Long ago an optics guru named Shack
Tutored a young professor named Jack,
Who, with his background electrical
Couldn't even ray-trace a spectacle,
Though he was traveling on an optical track.

Of optics Jack learned more and more,
And his respect for his mentor did soar,
Whose cover he'd have blown,
If only he could have known
Shack often peeked in his desk drawer.

Although it might sound somewhat bold,
Now that the truth has finally been told,
A desk drawer gets rewarded
Because Shack is awarded
The Society's coveted Medal of Gold.

This limerick by Gaskill alludes to a file of notes Shack kept in his desk, seemingly containing the answer to any question.

The Genesis of the Shack-Hartmann Test and the Shack Cube Interferometer

SPIE: The Shack-Hartmann test and the Shack cube interferometer are two of your many contributions to optical testing. Can you describe how they came about?

Roland Shack: The Shack-Hartmann test: One of our contacts through the Air Force was with the Satellite Tracking Facility at Cloudcroft, New Mexico. Satellite images were of course blurred by atmospheric turbulence, and Aden suggested that if we siphoned off some of the light going to form the image and put it through a Hartmann screen, we might be able to reconstruct the wavefront involved in forming the image and thereby do some image processing to improve it. He asked me to look into it.

The classical Hartmann screen consists of an opaque screen with holes in it. The beams that are transmitted through the holes are intercepted by a photographic plate some distance from the screen, and the path of each beam is determined. It is a simulated ray trace.

However, the classical Hartmann test is massively inefficient in using the light incident on the screen. Because the beams diverge somewhat after passing through the screen, the holes must have adequate spacing so that the beams will not interfere with each other. The fact that the source (the satellite) is somewhat extended also increases the spot size at the photographic plate. Also, allowance must be made for the deviations of the beams as well.

I was concerned because there aren't many photons available if most of them have to form the satellite image. The first thing that occurred to me was that I could increase the recording efficiency on the photographic plate by putting a small lens in each hole to focus the light onto the plate. It then occurred to me that there was no longer need for the screen between the holes. The lenses could be butted up against each other.

The Shack Cube Interferometer: Back when I was working at NBS I wanted to make what I called an Autostigmatic Microscope. This involved putting a beamsplitter between the objective and the eyepiece of a microscope with an illuminated pinhole on the side of the beamsplitter so that light from the pinhole would be focused on a reflective surface by the objective and returned through the beamsplitter to the eyepiece. When I tried this, the return beam was surrounded by a large halo of light from the reflection at the output surface of the beamsplitter, and it occurred to me that if I cemented a lens on that surface such that the pinhole was at the optical center of curvature of the surface, that ghost image would be in focus on the eyepiece side, providing a reference for the return beam from the objective and eliminating the need for a cross-hair.

Years later, at the Optical Sciences Center, I designed a null corrector for an astronomical mirror we were making, and a critical part of that null corrector was an autostigmatic cube to establish the axis. The pinhole was of course illuminated by a laser because of its efficiency and brightness. The light from the null corrector goes to the mirror under test, and the alignment consists of pointing the corrector so that the return image is free of coma.

I had a student working with me and I asked him to look through the eyepiece and tell me what the coma looked like as I made the adjustments. He was estimating the magnitude in wavelengths! I thought that was unusual, so I looked through the eyepiece myself, and discovered that, rather than focusing on the return image, he had focused on the image of the primary formed by the beamsplitter acting as a thick plano-convex lens, and thus was seeing the interference between the spot reflected by the spherical beamsplitter surface and the return image from the mirror. This could only happen with laser light.

And so the Shack cube interferometer was discovered.

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