|n 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.
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 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. 17:505-7, 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 oscillator—Optics
Lett., 24:631-3, 1 May 2000—and
demonstrated shortest pulses from a Q-switched solid-state laser—J. Opt. Soc. Am. B, 16:376-88, March 2000), average output power (27
W picosecond and 16 W femtosecond diode-pumped solid-solid state
lasers—Appl. Phys. B, 71:19-25, 2000 and Optics Lett.,
25:859-61, 1 June 2000), pulse repetition rates (up to about 60
GHz passively mode-locked Nd:YVO4 lasers—Appl. Phys. Lett., to be
published 12 October 2000—and more recently up to 77 GHz—Electronics Lett., in progress). Key for this success was a systematic
research effort to understand the underlying physics and scaling
What would you rate as your most difficult or trying professional
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.
Which of your professional achievements brings you the most
Excellent research, a great research team, motivated students, and
stimulating research collaborations.
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
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 work—the basic goal of physics.
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
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!
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 research—so that I can spend most of my time on research and not on general
management issues. With good performance—in 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 future—especially with a booming high-tech industry.
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 boys—Matthew age 3.5 years, and
Christopher age 21 months. In my remaining spare time (what spare
time?!)—in my spare time before having kids—I 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
My favorite Web-site:
The MIT faculty Newsletter, vol. XI, No.4, March 2000: http://web.mit.edu/fnl/women/women.html
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.
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
Dr. Ursula Keller
Institute of Quantum Electronics
Swiss Federal Institute of Technology (ETH)
Topics, August 2001
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