Emmett Leith

Inventor of Practical Holography
Emmett Leith Enlarge
Emmett Leith.

In 1952, twenty-five years old Emmett Leith was conducting highly classified research at the University of Michigan’s Willow Run Laboratories. This work – which utilized a novel process that mixed and recorded radar waves onto photographic film – was responsible for making a breakthrough in Cold War radar technology.

Little did Leith know that this early work would also establish the foundation for an innovation that would later inspire a global scientific movement – and make Leith well-known as the man who transformed the fledgling field of holography into a technology that has become integral to modern innovations in medical imaging, data storage, entertainment and other disciplines.

A Vision of the Future: Synthetic Aperture Radar to Holography

Leith joined the U-M Radar Laboratory of Willow Run Laboratories in 1952, with a Master’s degree in Physics. In later writings about his work, Leith said he was in the right place at the right time because of the very interesting work being done in the area of synthetic aperture radar (SAR). The Army wanted to achieve a high-quality imaging radar system – a goal thought to be impractical due to the size an antenna would need to be to achieve high resolution. No airplane could carry such a large antenna. However, if the antenna could be synthesized, such that a five-foot antenna could act like an antenna the size of a football field, perhaps such imaging could be accomplished. To simulate a larger antenna, radar returns were mixed with a local signal. For each transmitted pulse the returns were recorded on a photograhic film as a single line. This process continued as the airplane flew, which resulted in a film strip that contained no recognizable image, just like a hologram. This radar data then needed to be processed.

In the 1950’s, when the major developments in SAR occurred, computers were in their infancy and could not handle the gigantic computing task that was required to process the radar data. Based on discussions with R. Varian, one of the inventors of the kystron, two U-M scientists, Lou Cutrona and Wes Vivian, decided to accomplish the task using optical processing. When it came time to build the radar system, Emmett chose to work on the optical processor.

Within a couple years, Leith developed a completely new theory of SAR, based on physical optics. Leith stated, “this new way of describing SAR in combination with optical processing is what today would be called a holographic viewpoint.” Until it was proved, however, many scientists did not give the theory much credit.

The new radar system was ready to be tested in 1957. Eight flights yielded no images – which seemed to vindicate the critics of the new method and threaten continuation of the project. Flight nin, however, stated Leith, “produced some startling results. The terrain was beautifully mapped. The Michigan SAR system became famous.” Developed as part of Project Michigan, the new radar system allowed for high-quality mapping of enemy territory from a safe distance, penetrating even fog and darkness at longer distances than previously possible.

Making Holography a Reality

By 1960, Leith had turned his attention to holography, a technique that was first described in 1947 by Dennis Gabor. The concept was to record a wavefield on photographic film and then regenerate the wavefield at a later time by shining a beam of light through the photographic record, called a hologram. At first the technique was simply called wavefront reconstruction.

Gabor’s goal was to improve the resolution of an electron microscope. While moderately successful, the resulting images by Gabor were quite fuzzy, and had a twin image. Gabor could not correct this, and many scientists deemed the problem unsolvable. After 1955, holography went into a period of hibernation.

During this period, Emmett became intrigued with the principles of holography, which related to his own data processing work with synthetic aperture radar. He approached Juris Upatnieks, a scientist who had just joined the Willow Run lab in 1960, to get him interested in this new area. Upatnieks recalled that he was not initially impressed by Emmett’s description of wanting to take a transparency, record an out-of-focus image, and then take that recording and get a focused image back. However, after being shown a description of this process in the book, Principles of Optics by Born and Wolf (1959, now in its 7th edition), in which Gabor’s experiment was outlined, he was convinced.

The problem inherent in Gabor’s method seemed insurmountable, yet a moment of inspiration led to a unique approach, called carrier-frequency, or more popularly, off-axis holography. Key to this approach was the introduction of a second beam, called a reference beam, which passed around the object and impinged obliquely on the recording medium.

With this method, Leith recalled, “The image from the hologram was indistinguishable from the original object itself, and the process required no more coherence of the light than the original Gabor process. In fact, in further refinement, we devised a system that achieved carrier frequency holography, with coherence requirements that were about 15% less than required for Gabor’s original method.” This groundbreaking work, accomplished early in 1961, was published in 1962 in the Journal of the Optical Society of America (vol. 52). The basic problem was solved, yet further refinements and advances were needed before the technique would capture worldwide attention.

“This new way of describing SAR in combination with optical processing is what today would be called a holographic viewpoint.”

Lensless and 3D Photography

Emmett and Juris introduced display holography to the world in Fall 1963. It was publicized as lensless photography because a lens was not used between the object and the photographic plate. In the first step of this 2-step process, a negative is generated by splitting light into two beams: one beam, called the reference beam, travels directly to the photographic plate, while the other beam, called the object beam, first hits the object to be photographed before the reflected light waves reach the plate. Both beams meet at the photographic plate, creating a phenomenon known as interference. The result is an unrecognizable negative, described by Leith as “a hodgepodge of specks, blobs and whorls.” This is the hologram. In the second step, which is the reconstruction stage, the hologram is illuminated with a replica of the reference beam. Two images are formed: a virtual image behind the plate on one side of the illuminating beam, and a real image on the opposite side of the illuminating beam in front of the hologram that forms a sharp image on a screen. For the first time, holograms could now be made of arbitrary objects, not just photographic transparencies.

Eager for additional refinements, researchers called for a high-quality 3-dimensional display hologram, which had not yet been achieved (though the information to create the objects in 3D was present in the existing holograms). Emmett and Juris went to work making improvements on their technique, which would require use of the newly available laser to get the desired coherence of light. They presented their work at the Spring 1964 meeting of the Optical Society of America in Washington, DC. As recalled by Stephen Benton in the book, The Art and Science of Holography: A Tribute to Emmett Leith and Yuri Denisyuk (ed. H. John Caulfield), “Leith and Upatnieks gave a short oral paper on their 3D holograms, and invited the attendees to view a hologram in the hotel suite used by the Spectra-Physics company, who made most of the early holography-capable lasers. A line of optical scientists and engineers wound down the hallways of the hotel as they patiently waited to see the 3D images that were absolutely unprecedented in their realism and accuracy.”

The appearance of a crystal-clear 3-dimensional train completely transfixed the optical community, and led to press releases all over the world. Emmett and the hologram were featured in Life Magazine, and there were articles in Scientific American about the work.

These holograms had all of the usual properties of actual objects, including parallax. In fact, it was possible to peer behind obscuring structures to see what was hidden behind, just as if one were viewing the actual objects. Interestingly, the holograms were created such that by having even just a portion of the whole, the complete picture could still be generated.

Hologram of toy train Enlarge
This train, created April 1964, is one of the earliest three-dimensional holographic images.

Holography Becomes Practical

The startlingly realistic clarity of the three-dimensional holograms gave holography an appeal that reached outside the domain of the specialists, and called worldwide attention to this formerly esoteric subject. Whereas interest in holography had dwindled to just a few by 1960, by 1970, hundreds of worldwide research groups had turned their attention to coherent optics and holography. Improved techniques, new holographic materials and new application areas were explored by researchers around the world. The field quickly became multidisciplinary as applications in non-destructive testing of materials, medical imaging, display and entertainment, holographic optical elements, and optical data storage, drew in researchers from areas outside the traditional optics arena.

As affirmed by Gabor himself in his Nobel Prize lecture, the success of Leith and Upatnieks “was due not only to the laser, but to the long theoretical preparation of Emmett Leith, which started in 1955. This was unknown to me and to the world, because Leith, with his collaborators Cutrona, Palermo, Porcello, and Vivian applied his ideas first to the problem of the “side-looking radar” which at that time was classified… This was in fact two-dimensional holography with electro-magnetic waves… Their results were brilliant.”

“A line of optical scientists and engineers wound down the hallways of the hotel as they patiently waited to see the 3D images that were absolutely unprecedented in their realism and accuracy.”

Leith received numerous awards for his work, including the National Medal of Science in 1979, awarded by President Carter. Leith and Upatnieks were the first recipients of the R.W. Wood Prize, both were awarded the Inventor of the Year Award – presented by the U.S. Secretary of Commerce, and they received the ASME (American Society of Mechanical Engineers) Holley Medal. Leith was a member of the National Academy of Engineering, and was awarded the Frederick Ives Medal of the Optical Society of America, the IEEE Morris N. Liebmann Award, and The International Society for Optical Engineering (SPIE) Gold Medal. He was a fellow of the IEEE and Optical Society of America.

Leith earned more than 14 patents, including the first patent on holography, owned jointly with Upatnieks. This patent, filed April 23, 1964, was called, “Wavefront Reconstruction Using a Coherent Reference Beam.”

Expanding Uses for Imaging

The unifying principle between SAR and holography was coherent optics. Leith was a leader in the development of applications of coherent optics, and continued to work in areas having to do with imaging throughout his life. He maintained longstanding research relationships and friendships with several individuals who relied on his vast knowledge of the field to inform the progress of their research projects.

Dr. David Dilworth (MSE, EE and PhD, EE in ’83 and ’89), Director, Advanced Imaging Systems, of Argon ST, Inc., [formerly Daedalus Enterprises, Inc.], started working with Emmett as a PhD student in 1987, and through last December maintained weekly lab meetings with him. Their research focused on coherent optics, always with the goal of creating better images, particularly in the area of biomedical imaging. Dilworth and Leith own a patent that is related to the early detection of breast cancer.

Prof. Emmett Leith and research scientist Juris Upatnieks Enlarge
Prof. Emmett Leith and research scientist Juris Upatnieks

This process of imaging through highly scattering media, especially biological tissue, is known as photon migration, and has grown into an entire area of optics. Leith worked in this area since the early days in the late 1980’s. Using holographic methods, Leith stated that his goal was to “allow the seemingly impossible to happen – ideally, rendering biological tissue that was once impossible to see through to be as transparent as window glass. With such a technique, we could look into living tissue and discern anomalies such as malignant tumors. This ultimate goal is quite visionary; nonetheless, what has been achieved is encouraging.” A method potentially useful for detecting these and other anomalies, such as an increased blood supply to areas that might become cancerous later, was found to be effective up to a thickness of a few millimeters.

Emmett also worked with Dr. Brian Athey, Associate Professor of Psychiatry, Director, Michigan Center for Biological Information, and Director of the U-M Visible Human Project, on a variety of projects since the early 1990’s. In The Visible Human Project, Athey’s goal was to float a 3-dimensional image in front of a viewer, so that one could view it without any 3D glasses, and to replace anatomical with virtual dissections. “We are starting to use it in experimental classroom settings, and also for virtual surgery,” said Athey, who expects this to be in widespread use in 10-20 years.

Joy of Teaching and Love of Light

Emmett had a passion for optics that could perhaps only be matched by his love for teaching. He was instrumental in creating an optics program in the department during the 1960s, and took great joy in teaching the students. His graduate students often took part in Leith’s preparations. Marian Shi, a graduate student of Leith’s who is now a professor at Saginaw Valley State University, stated:

“The students in his lectures could almost hear the air crackle in his excitement, spreading his love of optics and reveling in the joy of scientific learning. Every Friday he spent hours preparing demonstrations that visually illustrated some of the more difficult concepts that he covered in class. I saw first hand what a thrill it can be to teach optics.”

Emmett Leith teaching a class Enlarge

His devotion to his students was expressed this past year when he underwent emergency surgery, yet the very next day asked to have his students’ exams brought to him to grade. He didn’t want the students to receive incompletes on their report cards.

Dick Zeck, who was a student, colleague, and friend of his for nearly 40 years, recalled that Leith refused to stay longer than 2 days at conferences because he wanted to return to his students. He also echoed the statements of many others present at Leith’s retirement reception when he said, “I am aware of no person or opportunity that ever compromised his integrity or professionalism. I learned much about proper thought and behavior by my association with him.”

Former student Jin Chang, now COE and president of General Scientific Corporation (parent company, Surgitel) in Ann Arbor, said that “Emmett really taught me how to live my life.” Chang now tries to help others, as Emmett helped him as a poor graduate student.

Rod Alferness, a student of Emmett’s who is currently Senior Vice President for Research at Bell Labs, has done pioneering research in the area of wavelength switched optical networks. He invented devices that form the basis for many of today’s wavelength division multiplexing (WDM) optical networking systems, and holds more than 35 patents. He said that by working with Emmett, he learned, “It’s about ideas. It’s about coming up with great, true ideas. I learned the joy of inventing and innovation, which has been valuable throughout my career.”

Alferness echoed many other student comments in their appreciation for Emmett’s excitement and amazement at what he was able to do with light, saying:

“A line of optical scientists and engineers wound down the hallways of the hotel as they patiently waited to see the 3D images that were absolutely unprecedented in their realism and accuracy.”

“Emmett was always appreciative of the exciting phenomenon of light. He took a fundamental understanding of light and from it invented ways to use light as, for example, a computer to process complex radar signals to produce spectacular surface images and, much more easily appreciated by the public, invented practical holography that allows three-dimensional images to be stored on film and recreated. His ideas and the things that he made possible from them were very powerful.”

Prof. Duncan Steel, Robert J. Hiller Professor of Engineering and Director of the Optics Laboratory at U-M, credits Leith with making Michigan the home of innovation in optics, which has since established new frontiers in the ultra-fast science and high-power laser areas.

Prof. Leith contemplates the valves recently installed in the laboratory Enlarge
Prof. Leith, known for his sense of humor, contemplates the valves recently installed in the laboratory. A trickle of He-Ne radiation amazes Prof. Leith, and with both valves open, an astonished Prof. Leith sees the full output of the He-Ne and Argon lasers on tap.

Leith Remembered

Emmett loved his work, and he happily brought his accumulated knowledge to bear on any topic being discussed. He also brought the fruits of his gardening to many of these discussions. His students and colleagues recall fondly the delicious tomatoes and fruit he would bring to the weekly group meetings. He may have been the only Michigander to grow an orange tree in his backyard, which he kept alive for many years through the winter by building a unique greenhouse around it – a house that he expanded each year as the tree continued to grow.

Emmett was a remarkably unassuming gentleman, who was known for his quiet ways, sense of humor, cheerfulness, and by the select few who could truly appreciate it, his brilliant mind. His students and colleagues were privileged to have caught a glimpse into aspects of both his personality and intellect. For some, it changed the course of their lives. In solving the problem of practical holography, he changed the future of imaging technology, and affected millions of lives.