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

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[9]: 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[7]: 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[10]: 2068-76, October 1991).

  What 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.

  How 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.

 What 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 laser pulses.

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 this goal.

  What 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.

  Which 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.

  Aside 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
Institute Professor
Research Laboratory of Electronics
Massachusetts Institute of Technology
Cambridge, MA, USA