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

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INTERVIEW with Dr. Ursula Keller

ESI Special Topics, August 2001
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In our analysis of high-impact researchers in the field of optoelectronics, Dr. Ursula Keller is ranked third, with 63 papers cited a total of 1,097 times. In addition to being a full professor of experimental physics at the Swiss Federal Institute of Technology in Zürich (ETH), Dr. Keller is the head of ETH’s Ultrafast Laser Physics Laboratory. Prior to joining ETH in 1993 as an associate professor, she was a member of the technical staff at AT&T Bell Laboratories in Holmdel, NJ. In this interview, Dr. Keller discusses the influences that have shaped her career, and the impact of her work in her field. 

ST:  How did you get started in your field, and what prior research or whose prior work helped to start you on your way?

I was born in Switzerland on June 21, 1959 and grew up in Zug, Switzerland, about 30 km south of Zürich. I graduated from the ETH in 1984 with a diploma degree (similar to a masters) in physics. From late 1984 to 1985, I worked on optical bistability at Heriot-Watt University in Edinburgh, Scotland. Then I moved to Stanford University in Stanford, CA and earned my M.S. and Ph.D. degrees in Applied Physics in 1987 and 1989, respectively. My doctoral thesis was done under the supervision of Prof. Dave Bloom, investigating optical charge and voltage probing of GaAs integrated circuits. For my first year at Stanford I held a Fulbright Fellowship and for the following year I was an IBM Predoctoral Fellow. I very much enjoyed my time at the Ginzton Lab and developed many good friendships there. I was also encouraged Dr Ursula Keller by Dave Bloom, Bob Byer, Steve Harris, Geraldine Kenney Wallace (a visiting professor from Toronto), and many others to give my best and excel beyond my own expectations. Looking back, I see this experience as a key event in my achievements since then. I was also fortunate that Dave Auston (at that time still at Bell Labs) made it possible for me to become a summer student at Bell Labs in 1996. This was also a perfect excuse to drive across the U.S. (twice) in an old station wagon (which of course also broke down at least twice).

In 1989, I became a Member of Technical Staff (MTS) at AT&T Bell Laboratories in Holmdel, New Jersey. Having had a great Bell Labs experience as a summer student, this was basically my dream job. It also put me right in the midst of the challenges for dual-career couples, as my new spouse and I decided to maintain a bi-coastal marriage. Living apart had the advantage that there was plenty of time for research, and also afforded the opportunity for many adventurous rendezvous around the USA and the world. At Bell Labs, I conducted research on photonic switching, ultrafast laser systems, and semiconductor spectroscopy. During this time I also started my work on semiconductor saturable absorber mirrors (SESAMs) to passively mode-lock solid-state lasers. Previous attempts to passively mode-lock diode-pumped solid-state lasers resulted in Q-switching instabilities, which at best produced stable mode-locked pulses within longer Q-switched macropulses (i.e. Q-switched mode-locking). The SESAM device was a breakthrough resulting in the first demonstration of self-starting and stable passive mode-locking of diode-pumped solid-state lasers with an intracavity saturable absorber in 1992 (Optics Lett. 17[7]:505-7, 1 April 1992).

In March 1993 I was appointed an Associate Professor and in October 1997 I became a Full Professor in the Physics Department at the Swiss Federal Institute of Technology (ETH) in Zürich, Switzerland. My current research interests are in ultrafast lasers, attosecond science, spectroscopy, local probes and novel devices for applications in optical information processing, communication, and medicine. Together with my research team at ETH we have continued to push the frontiers in passively mode-locked and Q-switched solid-state lasers in terms of pulse duration (demonstrated shortest pulses directly from a laser oscillatorOptics Lett., 24[9]:631-3, 1 May 2000and demonstrated shortest pulses from a Q-switched solid-state laserJ. Opt. Soc. Am. B, 16[3]:376-88, March 2000), average output power (27 W picosecond and 16 W femtosecond diode-pumped solid-solid state lasersAppl. Phys. B, 71:19-25, 2000 and Optics Lett., 25[11]:859-61, 1 June 2000), pulse repetition rates (up to about 60 GHz passively mode-locked Nd:YVO4 lasersAppl. Phys. Lett., to be published 12 October 2000—and more recently up to 77 GHzElectronics Lett., in progress). Key for this success was a systematic research effort to understand the underlying physics and scaling issues.

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

The pressure for success in the academic world has become so severe that sometimes ethical standards start to crumble. World-record results, for example the shortest laser pulse, draw a lot of attention and also result in a high citation index. But how far do you want to go for a world-record result? I was pretty amazed to see first-hand what competing groups are willing to do to be first. Is it O.K. to reference prior work not at all or out of context to give the impression of being first? When I started life in the academic world, I was not really aware of these issue.

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

Excellent research, a great research team, motivated students, and stimulating research collaborations.

ST:  What impact might your work and research advances in your field have on the general public?

Short laser pulses are being used in many fields that could have a direct positive impact on the quality of life. Certainly the most direct one would be medical procedures and diagnostics. Short pulse lasers are being used to detect cancer cells, measure bio-chemical events, image live cells and organisms, investigate genetic issues, perform advanced surgical procedures in the eye, brain, and other areas. My dream would be an ultrafast laser that would cure the common cold, but that is still pretty far in the future.

On a more industrial level, ultrafast lasers are being used in chemical and semiconductor measurement instruments, digital project displays, and of course in the increasing push for ultra-high-speed bandwidth fiber transmission systems. Basically all of these help advance the bandwidth revolution which we are in the middle of currently.

In the big picture ultrafast lasers are an important tool to measure phenomena which are happening at the borders of our perception. This leads in general to new discoveries and new understanding of how things workthe basic goal of physics.

ST:  Did you expect your work to become highly cited, or is this surprising to you?

I knew that my citation index is above average, but I was surprised to hear that the ISI analysis places me among the top 5 most-cited researchers publishing in the field of optoelectronics in the past decade.

ST:  What lessons would you draw from your work to pass on to the next generation of researchers?

Do good work, hang in there, play hard, but play fair!

ST:  If you had the power to make a single, sweeping change in the way that scientific research is conducted and presented, what would it be?

Long-term funding support with less bureaucratic requirements. Actually, my dream is to have enough money to fund my own researchso that I can spend most of my time on research and not on general management issues. With good performancein terms of publications, citation index, etc.we should have more freedom in our research efforts. Funding agencies should not micromanage good researchers. This actually results in wasted money and time for everybody involved. The worldwide tendency for less support of university research will make the academic career less attractive in the near futureespecially with a booming high-tech industry.

ST:  Would you like to leave any other comments about your work or share a personal side of yourself?

My personal note for dual career couples:

Switzerland also turned out to be the solution to my bi-coastal marriage, as my spouse Kurt Weingarten used it as an excuse to start his own company, Time-Bandwidth Products, where I also serve as a scientific advisor on the Board of Directors. In our spare time we have also managed to create two boysMatthew age 3.5 years, and Christopher age 21 months. In my remaining spare time (what spare time?!)—in my spare time before having kidsI enjoyed many mountaineering sports, especially ski mountaineering, and many water sports, such as scuba diving and wind surfing. Presently I try to spend most of my non-work-related time with my kids. Based on my experiences, I feel that balancing a career, a spouse’s career, and a family is not only possible but fun and rewarding (but not necessarily relaxing), and would like to provide encouragement to women everywhere to consider this option. In the "big picture" I would like to see better infrastructure for childcare, so that professional women have less pressure to sacrifice their careers.

My favorite Web-site:

The MIT faculty Newsletter, vol. XI, No.4, March 2000:

My research team:

I currently supervise about 20 postdoctoral and graduate researchers. To date I have graduated eight graduate students and 14 Diploma (Masters) students. Two of my senior researchers finished their "Habilitation degree," resulting in a full professor position at the University of Karlsruhe and a staff research position at the PTB in Braunschweig.

My awards:

  • 1985: Fulbright Fellowship for the first academic year at Stanford
  • 1987: IBM Pre-Doctoral Fellowship for 1987-1988
  • 1998: Carl Zeiss Research Award for pioneering work in novel mode-locking and Q-switching techniques using SESAMs.
  • 2000: LEOS distinguished lecturer award for 2000 and 2001

My professional society activities:

I am a member of the OSA, IEEE, European Physical Society (EPS), the Swiss Physical Society (SPS), and the Swiss Academy of Technical Sciences (SATW). Since 1998 I have been an elected EPS board member in the quantum electronics division and since 2000 an elected member of the IEEE LEOS Board of Governors. I have been a topical editor of Applied Physics B since 1994. Since 1993 I have served on many program committees for CLEO, QELS, OSA Annual Meetings, EQEC, CLEO Europe, Ultrafast Electronics and Optoelectronics, Ultrafast Optics, Advanced Solid-State Lasers, and FST Japan. I was the program chair and general chair of Advanced Solid-State Lasers in 2000 and 2000 respectively. In addition, I jointly organized, with François Salin, the Ultrafast Optics conference in Ascona, Switzerland in 2000 (see also Appl. Phys. B 70, Supplement June 2000). I chaired the OSA 1998 Lomb Medal Committee.

Dr. Ursula Keller
Institute of Quantum Electronics
Swiss Federal Institute of Technology (ETH)
Zurich, Switzerland

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

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