Theodor Wolfgang Hänsch shared one of the two 2005 physics prizes with John Hall of the USA for their independent development of laser-based precision spectroscopy. The other prize was awarded to Roy Glauber (USA) for his theory on the behaviour of photons. Light, like radio waves, is a form of electromagnetic radiation. Different colours come from light at different frequencies. Hall and Hänsch have made it possible to measure frequencies with an accuracy of fifteen digits, allowing lasers to be fine-tuned to produce extremely narrow-band radiation.
Hänsch was born in Heidelberg, Germany, in 1941. The family lived in a house that had belonged to chemist Robert Bunsen, and Theodor’s father brought home a Bunsen burner to demonstrate some simple chemistry, burning table salt and explaining the sodium caused a bright yellow flame. “It was obvious to me that I had to find out more about light and atoms”, Hänsch recalls. At 16, he built a Geiger counter and set his sights on becoming a nuclear physicist. Hänsch was educated at the Helmholtz Gymnasium and progressed to Heidelberg University, gaining his PhD in 1969. In 1970, he left Germany to join Arthur Schawlow, co-inventor of the laser, at Stanford. There Hänsch invented a laser with a high spectral resolution (i.e. all the photons emitted had nearly the same energy, to within one part in a million).
Based on a laser he had seen at Bell labs, Hänsch and Schawlow invested in a similar device. Hänsch used a pocket telescope to spread the beam and observed a dramatic improvement in the laser line width, reducing the spectral width to 0.0004 nm. He devised a scheme for saturation spectroscopy – a technique later known as Hänsch-Bordé method, since Christian Bordé in Paris had pursued similar ideas. In 1973, Schawlow and Hänsch were named California Scientists of the Year. Hänsch remained at Stanford, rising to professor in 1975, before returning to Germany in 1986. In Germany, Hänsch joined the Ludwig-Maximilians University of Munich as a professor and set up a new laser spectroscopy lab at the Max-Planck-Institute in Garching, where he is now a director.
It was in Garching, at the end of the 1990s, that Hänsch developed the ‘frequency comb synthesiser’, which produces frequency measurements for light across the spectrum so precise – to one part in a hundred trillion – that it is possible to search for changes in the fundamental physical constants of the universe over time and, more prosaically, develop accurate clocks and improved global positioning system (GPS) technology. Hänsch’s team also created a Bose-Einstein condensate in 1998, and created the first continuous wave atom laser in 1999. He has received several honours, including the Gottfried Wilhelm Leibniz Prize, the highest honour awarded in German research.
This text and the picture of the Nobel Laureate were taken from the book: "NOBELS. Nobel Laureates photographed by Peter Badge" (WILEY-VCH, 2008).
Picture: © Peter Badge/ Foundation Lindau Nobelprizewinners Meetings at Lake Constance |