Emil Wolf, a research fellow at Manchester University, is spending Easter vacation with his wife at her parents’ house in southern England. Vacation is not the right word. His days are spent correcting final proofs for Principles of Optics, a massive treatise he’s coauthoring with physics Nobel laureate Max Born.
With the end so close after almost eight years, Wolf realizes an entire batch of proofs is missing. Dreading further delay, he returns to Manchester to check in with the physics department’s secretary. She assures him everything has been sent along. But Wolf’s doubts are not easily dispelled—the secretary’s lack of tidiness is axiomatic. Several days later, he infiltrates her office while she’s out to lunch.
Wolf locates the missing proofs, and in the process makes a surprising discovery. Tucked away in an office cupboard is a letter addressed to him from Robert Hopkins, the director of the Institute of Optics:
Dear Dr. Wolf, We are trying to find someone who works on coherence theory. I’ll be in England in two weeks and I’d like to discuss the possibility of your coming to Rochester.
“That was the letter, just sitting there, and I almost didn’t get it,” recalls Wolf, a half century later. “I nearly panicked—there were no e-mails in those days, no faxes. Thankfully I managed to get a hold of Hopkins before he left for England.”
As a World War II refugee from Prague, Wolf had faced an uphill battle trying to secure a faculty appointment in the United Kingdom. His postdoc position in Manchester was slated to end in 1958 and the prospects for employment worried him.
“Happening upon that letter completely changed my life—I met with Hopkins that July and he offered me the job,” says Wolf. “Can you believe that? I barely made it.”
Since that life changing moment, Wolf has come to be recognized as one of the world’s foremost physical optics experts, especially in the areas of coherence, polarization, and diffraction. His research—including three books and more than 400 scientific papers—has been crucial in many fields, including holography, laser science, medical imaging, as well as cryptography, radio astronomy, and the search for long-buried fossils.
“Emil Wolf has been the doyen of physical optics for more than 50 years, responsible more than anyone for putting the theory of optical coherence and the theory of diffractive optics on a firm foundation,” says Peter Knight, a professor of quantum optics at Imperial College, London, and a past president of the Optical Society of America.
Last fall, Wolf’s lasting commitment to optics was on striking display at the society’s annual meeting where he was honored for having presented at least one scientific paper at each conference for 50 consecutive years.
And the number of papers Wolf has presented annually trends upward over time. While he typically gave one or two papers during his early career, over the past decade he has been an author or coauthor on as many as nine.
Wolf’s passion for physics and optics stems from an early interest in pure mathematics, which he attributes to having had an excellent math teacher in high school.
His eventual transition to theoretical optics in graduate school made perfect sense given that mathematics is what Wolf calls the “natural language of physics.”
And since coming to Rochester in 1959, Wolf, now the Wilson Professor of Optical Physics, has never stopped exploring the intricacies of that language.
Principles of Optics was completed the same year Wolf arrived in the United States, and it quickly became, and has remained, one of the landmark texts in optics and one of the past century’s most cited science books. Now in its seventh edition, it is popularly referred to as simply “Born and Wolf” or “The Bible.”
“Through ‘Born and Wolf,’ generations of students and researchers have obtained a rigorous optics education,” says William Phillips, a Nobel laureate and researcher at the National Institute for Standards and Technology.
Perhaps Wolf’s most significant contribution to the book was a chapter on the coherence properties of light.
To explain coherence, Wolf often uses an analogy of marching soldiers: “Imagine a contingent of 1,000 soldiers walking perfectly in step across a bridge. That’s an example of coherence. If they are drunk and wander randomly across the bridge, that’s incoherence. But if some walk in step, and others wander, you have partial coherence.”
Coherence describes the degree to which atoms, or photons in the case of light, are in sync with one another. A 60-watt lightbulb emits light randomly, or incoherently, while the photons from a laser are “in step” with one another and therefore coherent.
“Hopkins showed real foresight,” says Wolf. “He thought lasers and coherence were the areas the Institute of Optics needed to be concentrating on, and he realized this much earlier than scientists at other universities.”
Wolf and Hopkins organized the first-ever Conference on Coherence, which took place in Rochester in June 1960. Just weeks later the first laser was operational, and scientists flocked to the chapter on coherence in “Born and Wolf,” as it offered the only thorough treatment of a subject central to understanding key features of laser light.
The conference—later renamed the Conference on Coherence and Quantum Optics—likewise gained long-term traction, taking place every 5 to 6 years, with the most recent in June 2007. Although Wolf no longer organizes the conference, his second book, Optical Coherence and Quantum Optics (Cambridge 1995), emerged from research presented at the conference. Wolf wrote the book with his late friend and close colleague, Leonard Mandel, who was the DuBridge Professor Emeritus of Physics and Optics when he died in 2001.
As virtually everyone in the field of optics will attest, Wolf has worked tirelessly to advance the scientific understanding of optics.
In recognition of the seminal contributions he had made to the study of light, he was named an honorary member of the Optical Society of America in 1987. The distinction placed him in a very exclusive club. Today there are only 10 living members, eight of whom are Nobel Prize winners, including Steven Chu ’71, now serving as the Obama administration’s energy secretary.
And over the past two decades Wolf has shown no signs of slowing down.
“In 2005, the book Tribute to Emil Wolf was published, and when it was being put together, some of us suggested the subtitle, ‘A Mid-career Perspective.’ ” says Paul Scott Carney ’99 (PhD), a former student of Wolf’s who is an associate professor of electrical and computer engineering at the University of Illinois at Urbana-Champaign.
In 2007, Wolf released his third book, Introduction to the Theory of Coherence and Polarization of Light (Cambridge), which received the Joseph W. Goodman Book Writing Award from the optical society last October. The biennial award recognizes an outstanding book published in the last six years in the field of optics.
But if Wolf is acknowledged for one thing above all else, it’s for his role as a teacher.
Last fall Wolf intended to teach a graduate course based on his recent book, but the idea was placed on hold because of his wife Marlies’s poor health. Miguel Alonso ’96 (PhD), an associate professor of optics at Rochester and a former student of Wolf’s, stepped in and decided to offer an independent study focused on the book.
“Two of my graduate students had really wanted to take Emil’s course,” says Alonso. “So when it was cancelled I decided to offer a reading course. I told Emil about it, and he came to pretty much every session. By the end, it was almost like he was the instructor.”
In November 2008, Wolf was notified that the optical society’s foundation was working to establish an annual student paper competition in honor of his decades of teaching, achievements, and service. The first award will be given at the society’s 2009 annual meeting.
“He’s a truly inspirational figure,” says Knight, a cochair of the fundraising committee for the competition.
“It was a complete surprise when I heard about the effort to establish a competition in my name,” says Wolf. “I had no idea that so many of my former students and friends were involved in this. It’s very touching.”
Even now, at 86, Wolf radiates real excitement when discussing his latest research.
What drives him so ceaselessly?
The answer is elegantly simple: “I find scientific work extremely rewarding. The things I come across—I love it!” says Wolf. “And I wouldn’t dream of giving it up.”
Evan Wendel writes about engineering for University Communications.