Biographical
I was born in Heidelberg, Germany, on October 30, 1941. My parents had moved there from their native Breslau a few years earlier. As far as I can tell, I am the only academic in our family. My father Karl Hänsch was a businessman engaged in the export of farming machinery, while my mother Marta raised her three children as a house wife. My younger brother Julius entered the book printing business, and my sister Lucia married a fellow physics graduate student and now helps run a small electronics engineering company.
Growing up during and after the second world war left some vivid memories. I can still see our family huddled together in the basement bomb shelter of our home in Heidelberg listening to the piercing sound of air raid sirens. After the war, our family had lost its estate in Breslau, and we had to share our small ground floor apartment in Heidelberg with some war refugees as subtenants. Without childhood diversions such as television, my brother and I gained a strong sense of independence and adventure by playing in the bombed ruins at the nearby railway station or exploring the many hiking trails on the slopes of the Gaisberg and Königstuhl. My father had long been disillusioned with the Nazi political leadership and raised us as rebels in spirit, distrusting any official authority.
My father also kindled my early interest in science. During the first world war, volunteering at a pharmacy, he became interested in medicine and chemistry. In Heidelberg we lived at Bunsenstrasse 10, in the house that had once belonged to the chemist Robert Bunsen. When I was about six years old, I asked my father what Bunsen had done to have a street named after him. On the next day he brought home a Bunsen burner which we connected to the gas stove in the kitchen. With a sprinkle of table salt, the blue flame turned to a bright yellow. My father explained that this is the characteristic color emitted by sodium atoms that are excited in the flame. It was obvious to me that I had to find out more about light and atoms. A little later, my father took me to visit the metallurgical laboratory of the Heinrich Lanz AG in Mannheim, where I was impressed by researchers in white lab coats who allowed me to look into their fancy microscopes. At a time when other boys dreamt about steering steam locomotives, I started to see myself as a future scientist.
In 1952, I entered the Helmholtz Gymnasium in Heidelberg, then located at the Kettengasse in the old town below the castle. Although the school emphasized modern languages and science, my father enrolled me in a rather small class with Latin as the first language to maintain my option of studying medicine. During the later years we enjoyed some remarkable teachers. Dr. Mampel, our physics and chemistry teacher, gave me free reign of the school’s collection of demonstration apparatus, and Dr. Biser, a Kaplan at the nearby Jesuitenkirche, who later became an eminent religious philosopher, turned the obligatory religious studies into a fascinating course on Western philosophy.
Early on, my interest in science dominated my activities outside school. I eagerly read popular science and science fiction books from the public library until I learned how to check out textbooks from the University library. I also liked doing experiments with my own hands. Intrigued by the world of chemistry, I started to spend my weekly allowance in pharmacies willing to sell substances like fuming nitric acid or white phosphorous to a young boy who stored his growing collection of chemicals in the bedroom of his parents. After an intimidating accident with bomb-making materials, my interests moved from chemistry to physics and electronics. Around 1957, I acquired an old cold cathode X-ray tube which I operated at home after winding a large Ruhmkorff-style induction coil. I also built a transistorized Geiger counter to perform experiments with a radioactive sample of 0.1 millicurie of Mesothorium which I had bought at a factory for radioactive luminous paint. To calibrate the Geiger counter, I went to the nuclear physics laboratory of Professor Otto Haxel at the University of Heidelberg, where an assistant was very kind and willing to introduce me to the real world of physics research. At that time, I set my sights on becoming a nuclear physicist and university professor.
Study at the University of Heidelberg
After the Abitur in 1961, I enrolled at the University of Heidelberg as a physics student. During the first two years most of my energy went to the study of mathematics. The lectures on physics and chemistry seemed like entertaining diversions by comparison. I was awed by the power and elegance of pure mathematical reasoning. But after a while I realized how much the complexity of an abstract formalism can sometimes distract from true physical insights. Since then I have acquired a compulsion to always try and construct the simplest possible intuitive model to “understand” a physics phenomenon. Such models have often helped me to perform quick order of magnitude estimates and to rapidly weed out half-baked ideas. Playing around with intuitive concepts I frequently arrive at interesting ideas only to find out that the results have been worked out long ago and are well known. But every once in a while I have experienced the immense joy that comes with some entirely new insight or invention.
After the Vordiplom in 1963, I enrolled in the Betatron laboratory of Professor Hans Kopfermann for the Grosspraktikum, an initial laboratory project of about six months. Unfortunately, Professor Kopfermann had died just before I could begin work on my assignment, the construction of a transistorized fast linear gate for a semiconductor detector of alpha particles which I quickly completed. In the spring of 1964, I attended my first meeting of the German Physical Society. Listening to different talks in a nuclear and particle physics session describing the work of large teams working at big machines, I lost some of my enthusiasm for this kind of research.
Instead, I became intrigued by the growing excitement about lasers which had been invented a few years earlier. In the neighboring Institute of Applied Physics at Albert-Überle-Strasse, Professor Christoph Schmelzer had started to design a linear accelerator for heavy ions that was later realized at the GSI in Darmstadt. Since he felt that lasers might help to synchronize the phases of the individual resonators, he had hired Dr. Peter Toschek, a former student of Professor Wolfgang Paul in Bonn, as an assistant to set up a laser group in Heidelberg. Visiting this laboratory I was awed by the sight of a helium neon laser with its glowing discharge tube emitting an intense collimated beam of red laser light that produced an otherworldly speckle pattern. I sensed a large unexplored new world, and I instantly decided to switch fields. Fortunately Peter Toschek accepted me into his group so that I could pursue my two years of diploma research on gas lasers. Since commercial lasers were not yet available, we had to build everything ourselves, including the glass discharge tubes with their electrodes and Brewster windows, the gas filling stations, the high voltage power supplies, and even the dielectric mirrors and their adjustable mounts. In hindsight, this was excellent training for a budding experimentalist. My adviser was a scholar of high intellectual standards who made sure that we kept track of every single publication in the emerging field of lasers and quantum electronics. In my diploma research, I studied saturation effects in the gas laser medium by observing the light emitted spontaneously to the side. In the end I was able to determine a number of previously unknown radiative transition rates in the neon atom.
After receiving my physics diploma degree in 1966, I continued to study laser saturation phenomena in my thesis research. I had become intrigued by the sharp central Lamb dip, a drop in laser power, that Ali Javan had first observed when scanning the frequency of a single mode gas laser across the Doppler-broadened gain profile. The Lamb dip allowed a new kind of nonlinear Doppler-free high resolution spectroscopy, albeit limited to the study of laser transitions or to the “inverted Lamb dips” produced by molecular absorption lines in accidental coincidence.
In my own experiments, I studied the cross saturation of two coupled laser transitions in neon that share the same lower level. Soon, I observed strange line asymmetries that could not be understood within a hole burning model. I tentatively ascribed the observed phenomena to Raman-like two photon transitions and the dynamic Stark effect. After laboring for considerable time as a theorist I was able to explain the observations quantitatively with a semiclassical model that relied on the density matrix formalism to account for quantum interference effects in coupled three-level systems. This work, published in 1970 with Peter Toschek, is still cited frequently today, because it laid the groundwork for the understanding of phenomena such as lasers without inversion, electromagnetically induced transparency, and slow light. In January of 1969, I received my doctor degree from the University of Heidelberg (Dr. rer. nat., “summa cum laude”), and I continued to work in Heidelberg for another year as an assistant of Professor Schmelzer. Aspects of coherence and quantum interference have remained a recurring theme in my later research, with intuitive insights from classical wave optics often guiding my thoughts and ideas.
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Source:
https://www.nobelprize.org/prizes/physics/2005/hansch/biographical/
