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ESI Special Topic of:
"Optoelectronics," Published August 2001

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INTERVIEW with Dr. Henry Kapteyn

ESI Special Topics, September 2001
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In this Special Topics interview, Dr. Henry Kapteyn of the University of Colorado at Boulder Department of Physics discusses his highly cited work in the field of optoelectronics. Thirty of Dr. Kapteyn’s papers were included in our analysis of high-impact optoelectronics research. These papers have been cited a total of 1,021 times, making Dr. Kapteyn one of the top 5 most-cited optoelectronics authors of the past decade. Dr. Kapteyn came to the University of Colorado’s Department of Physics from the Department of Electrical Engineering and Computer Science at the University of Michigan in 1999. He is also a Fellow of JILA, an interdisciplinary graduate and research institute in the physical sciences, which is operated jointly by the University of Colorado and the National Institute of Standards and Technology (NIST).

ST:  What unexpected or serendipitous events arose in the course of your research?

For the most part, research is a matter of persistence and hard work. However, there have been a few serendipitous events in my research career. Probably most important was meeting my wife and colleague, Margaret Murnane, as a graduate student at Berkeley. We have built our research careers together and have an unusual style, complementing each other in a very effective way. This has lead to over 100 jointly-authored publications. Most recently, Margaret was named a John D. and Catherine T. MacArthur Foundation fellow. Since one cannot apply for these awards, this would definitely qualify as a "serendipitous" event that will help our research tremendously in the coming years.

I can also point to a few specific unexpected results that accelerated our work. When we first started as independent researchers at Washington State University, at one point our work on ultrashort pulse lasers involved an extensive search of possible design parameters. A student that we had hired for clerical work to type in a large set of parameters entered some information that we had not actually asked her to. This information turned out to be very useful, and helped lead us to an important advance in laser technology.

This work in turn generated so much interest from our colleagues that at one point I wrote a 40-page "manual" on what we had learned about implementing a very short-pulse laser. Although we never published this work formally—we simply started handing it to people who asked for information—this paper became widely distributed and copied in the field of ultrashort pulse lasers. This document played an important role in fueling rapid progress in the field of ultrafast science during the 1990s. Our best estimate is that several thousand people obtained copies of this document, and more than a thousand of these ultrashort-pulse "Mode Locked Ti:sapphire Lasers" were built by researchers based on our design. Thus, one of our works that altered to course of laser research in the 1990s was never even published! We had never anticipated such a reaction to this document.

More recently, our research has been in developing new ways of generating very short pulses of x-rays. Part of our research philosophy has been to be at the forefront of developing new (laser) technologies, and to be perfectionist in this area. The result is that (although it doesn’t always seem that way to our students) our students get a lot of "lab time," increasing the probability of obtaining the serendipitous result. Our recent results in this area published in Science and in Nature both were in some part the result of searching in a new range of "parameter space" that no one had studied before.

ST:  What role did practical support (facilities, funding, etc.) play?

Our work in developing new laser sources is very equipment-extensive and reasonably demanding in terms of the laboratory environment. Thus, practical support is essential. In terms of funding, much of our work was done with National Science Foundation and Department of Energy support, as well as in the beginning from "startup" funding from the University. Our work also depends critically on technical support—machine shops and electronics shops with knowledgeable and productive people. When we started out as independent researchers, we found the shop personnel at Washington State were very helpful. Most recently, we moved to JILA at the University of Colorado because of its (well-deserved) reputation of having support services for experimental science that are world-class and second to none. Our move to Colorado required a complete rebuild of three semi-truck loads of equipment from our labs; our first paper on work done here was submitted less than 6 months after we arrivedand recently appeared in Nature. This rapid reconstruction and progress could not have happened without excellent technical support.

ST:  How do you see the current state of affairs in your field and its prospects for the future?

Extremely exciting! Margaret and I develop ultrashort-pulse lasers as tools for research, and also use them to study dynamic processes in material and chemical systems. I view this work as at the leading edge of perhaps the most defining characteristic of the times we live in: the quest for speed. Currently, the lasers we work with have made it possible for researchers to routinely study processes that happen on a 10-femtosecond time scale. 10 femtoseconds is 10^-14 seconds. To give a perspective on this number, the geometric mean between 10 femtoseconds and the age of the universe is a time of about a minute.

Femtosecond time scales correspond in a real sense to the fundamental "clock speed" of our everyday world; i.e. the time scale of molecular and electronic processes. Many chemical reactions, and thus even the basics of living organisms, happen on femtosecond time-scales. Current electronics is pushing from nanosecond into picosecond time-scales. Using an ultrashort-pulse laser as a "strobe light" to study these fast events, we are laying the groundwork for further technological advance, and for understanding our world at a fundamental level. More specifically, our work in generating short-pulse x-rays expands the region of the electromagnetic spectrum that we can use for this work, giving us fundamentally new techniques for observing dynamic processes. Using x-rays, it will also be possible to access even shorter, "attosecond" time-scale processes—we have just completed a set of experiments that have demonstrated that we can control the interaction of light with atoms on such an attosecond time-scale. To do this we learned how to generate and manipulate optical pulses as "waveforms," similar to what has been done with radio-frequency signals for decades. Using these optical waveforms, we can control how light pulses interact with matter in a much more precise way. This work is an example of how light pulses can control atoms and molecules, and may lead to new types of "coherent control" of chemical processes.

Nuclear and high-energy processes happen on even faster time scales, but our technology is very far from using these types of processes in small-scale, everyday devices or in information processing. Thus, I am looking forward to a future several decades from now where optoelectronic computers are orders of magnitude more complex than current computers, and operate on femtosecond cycle times.

ST:  What are the implications of your work for the future of your field in terms of clinical/therapeutic applications/products?

Ultrashort-pulse lasers are being studied for several medical applications. The two most advanced of these techniques are to use short light pulses as a "radar" to take micron-resolution three-dimensional images of the eye, and the use of these lasers in "two-photon microscopy," a technique that makes it possible to create sub-micron resolution 3-D microscope images. There are also possible surgical uses of these short-pulse lasers. I am not personally doing this work, though—I went into physics in part because there is no blood involved.

ST:  What would you rate as your most difficult or trying professional moment?

Several years ago, we had difficulties with a senior professor at another institution, after we moved from WSU. We were junior professors at the time, and he was in a position to harm and co-opt our research. This was an extremely trying situation that nearly prompted Margaret and I to quit academic research. Fortunately, we were "rescued" from this situation by an offer to move to JILA, a joint institute between NIST and the University of Colorado. The situation and the atmosphere in Colorado are as bright here as they were dim there.

ST:  Which of your professional achievements brings you the most satisfaction?

The field of laser science was attractive to me because developing a new tool for researchers can lead to faster progress in a variety of fields in the sciences; i.e. the impact of one’s work is multiplied by the hard work of hundreds or thousands of other scientists. The fact that this has happened, and that people in fields ranging from physics to chemistry to neurobiology are making use of lasers developed in our work, is very satisfying.

ST:  Aside from your scientific career, what is your greatest or most compelling ambition in life?

Like most scientists, I got into research to "make the world a better place," and science is my most compelling ambition in life. However, as well as my university research, I have started a small company in ultrashort-pulse laser technology, and hope to see it become successful. Also, I would hope that the example that Margaret and I give as a successful couple working in science will help to broaden the appeal of physical science, making it less of a "male domain" than it currently is.

Dr. Henry C. Kapteyn
University of Colorado
Department of Physics
Boulder, CO, USA

ESI Special Topics, September 2001
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ESI Special Topic of:
"Optoelectronics," Published August 2001

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