Wolfgang Kaiser
Honorary Degree Recipient
- Doctor of Science, Purdue University 1993
[Professor Kaiser's] insightful investigations in semiconductor physics, his landmark discoveries in the physics of lasers and their application to non-linear spectroscopy, and his pioneering work on stimulated Raman and Brillouin scattering and their time-resolved studies have made a profound impact on our understanding of condensed matter.
Professor Kaiser's association with Purdue dates to 1952 when he joined the physics department to work with one of us (HYF) as a Research Associate. His creative participation in the infrared investigations of semiconductors then in progress led to several major contributions during 1952-54. The infrared absorption spectrum of p-type germanium and the deep insights into its complex valence band; infrared absorption edge of n-type indium antimonide, its shift with increased electron concentration and its explanation in terms of electron degeneracy and very small effective mass; photoconductivity of Cu doped and Au doped germanium whose understanding led to sensitive infrared detectors - all first-rate discoveries - are now standard references in the literature on semiconductor physics.
In 1954 Kaiser joined the Signal Corps Engineering Laboratories, Fort Monmouth. His discovery of oxygen in crucible grown silicon was a triumph of scientific 'detective' work; guided by clever intuition, employing simple spectroscopic and analytical techniques, Kaiser solved a major puzzle in semiconductor technology. He demonstrated that oxygen from the quartz crucible enters silicon interstitially, that it can be converted into "thermal donors" and into "colloidal oxygen clusters", in a reproducible manner by thermal cycling at specific temperature ranges. He clinched his findings and their interpretation by his discovery of oxygen in germanium with a similar behavior pattern.
Kaiser joined the Bell Laboratories in Murray Hill in 1957 and remained there until 1964. One of his early achievements during these years was the resolution of the intriguing differences between the so-called Type I and Type II diamonds: he conclusively showed them to be due to the presence of nitrogen in the former, again with the use of spectroscopy and analysis of gaseous products extracted from diamonds. This was the period when the ruby and the He-Ne lasers were invented. Kaiser belongs to the early pioneers of this exciting period. He studied the fluorescence and optical maser effects in CaF2 : Sm2+ and the Stark effect of ruby emission lines. His work contributed to the rapid advances in this important field. He observed for the first time two photon absorption, CaF2 : Eu2+ being the system in which he demonstrated it. This work represents a beautiful experimental verification of a 1931 theoretical conjecture by Maria Göppert-Mayer; it signalled the establishment of a major branch of modern spectroscopy.
Kaiser returned to West Germany in 1964 as Professor of Physics in the Department of Physics, Technische Universitat München. Within a short time, he established a thriving center of research focussed on novel phenomena whose discovery and study were made possible by intense lasers. Stimulated Raman and Brillouin scattering; self-focussing of light; phonon life times deduced from time resolved Brillouin scattering; and molecular dephasing are among the many fundamental studies which emerged from his group under his creative, imaginative, and energetic leadership. Photochemistry of bacteriorhodopsin addressed on a femtosecond time scale; time-resolved spectroscopy of organic molecules and their reaction kinetics; and infrared spectroscopy of hot carriers in multiple quantum wells of semiconductors are further examples of the rich variety of problems investigated by Kaiser and the team of his talented students and associates.
Kaiser's many path breaking contributions to spectroscopic studies of matter and to spectroscopy itself have received international recognition. The Max Born Prize of the British and German Physical Society, the Lippincott Prize of the Optical Society of America, and his election to the U.S. National Academy of Sciences as a Foreign Associate bear testimony to his scientific eminence. By conferring on him a 1993 honorary degree of Doctor of Science, we express Purdue's pride in and admiration for his numerous creative contributions which have significantly advanced science.
From the nomination letter by Professors H. Y. Fan and A. K. Ramdas, October 6, 1992