unexpected or serendipitous events arose in the course of your
I had worked on the theory of mode-locking since 1974. At that time
the work of Shank and Ippen at Bell Laboratories, the first generation
of sub-picosecond pulses, created wide interest. My intention was to
develop an analytic theory of mode-locking in the Shank-Ippen system,
in which a laser-pumped dye provided the gain and a passive dye
provided the loss. The experimental results raised the question as to
how it was possible to generate picosecond pulses using media with
relaxation times in the nanosecond range. Part of the explanation was
provided by G.H.C. New of Imperial College, who simulated the process
numerically. He showed that the joint action of a saturating slow gain
medium and slow saturable absorber could provide a net gain window of
picosecond duration. My analytic theory ("Theory of mode-locking
with a slow saturable absorber," IEEE J. Quant. Electron.,
11: 736-46, 1975) was able to provide analytic relationships among
the parameters of the laser system. But before I worked out this
theory I analyzed a much simpler system with a saturable absorber that
had a relaxation time much shorter than the pulses generated by the
action of the saturable absorber ("Theory of mode-locking with a
fast saturable absorber," J. Appl. Phys. 46: 3049-58,
1975). No saturable absorber with these properties existed at that
time. The application of this theory had to wait until
"artificial" saturable absorber action with these properties
was implemented, which resulted in the 1991 paper, "Structures
for additive pulse mode-locking" (Journal of the Optical
Society of America B-Optical Physics, 8: 2068-76, October
role did practical support (facilities, funding, etc.) play?
My theoretical work in the last 30 years always addressed practical
problems arising in connection with the research on optical and
quantum optical systems. The existence of state-of-the-art
laboratories run by my colleagues and my students provided first-hand
information and inspiration for the theoretical work. Funding was by
the Office of Naval Research, the Air Force Office of Scientific
Research, and the National Science Foundation. It goes without saying
that without this support none of the work would have been possible.
do you see the current state of affairs in your field and its
prospects for the future?
My major concern is the demise or substantial reduction of basic
research in industrial laboratories. The changes in Lucent, Bell
Laboratories are just one of many examples. If the profit motive is
the only incentive, basic research does not pay for itself, since it
takes too many years to bear fruit. The organization that conducted
basic research loses control over its commercial use. Major thrusts in
basic research have to be reestablished, through government support,
and maybe through university-industry collaborations, also funded by
the government. The future of our advanced economy depends on it.
are the implications of your work for the future of your field in
terms of clinical/therapeutic applications/products?
My work on mode-locked pulses is a contribution, although a modest
one, to the development of laser sources for medical applications. My
colleague Prof. J. Fujimoto and coworkers have developed new imaging
techniques called Optical Coherence Tomography (OCT) for eye- and
subcutaneous diagnostics using the very broad spectrum of ultra-short
The millions of spectral lines of an ultra-short pulse, mode-locked
laser can be used as a set of standard frequencies if locked to an
atomic transition. Many laboratories around the world are now pursuing
would you rate as your most difficult or trying professional moment?
I still remember the campus unrest of the late ‘60s and early ‘70s
as the most disruptive in my career. It put into question the basic
principles on which our society is founded and on which the pursuit of
knowledge is predicated.
of your professional achievements brings you the most satisfaction?
At any professional conference today one may see the realization
and commercialization of many ideas on which my colleagues and I had
worked many years ago. A special gratification was to be the recipient
of the 1995 President’s National Science Medal. Having been expelled
from Yugoslavia in 1945 as an undesirable alien, I found pride and
solace by receiving this recognition in my adopted country.
from your scientific career, what is your greatest or most compelling
ambition in life?
To be, and have been, a dedicated teacher and family man, with
children who are able to forge their own way in life.
Dr. Hermann Haus
Research Laboratory of Electronics
Massachusetts Institute of Technology
Cambridge, MA, USA