Hänsch is Director of the Max-Planck-Institut für Quantenoptik (quantum optics) and Professor of experimental physics and laser spectroscopy at the Ludwig-Maximilians University in Munich, Bavaria, Germany.

In 1989, he received the Gottfried Wilhelm Leibniz Prize of the Deutsche Forschungsgemeinschaft, which is the highest honour awarded in German research.

The Nobel Prize was awarded to Professor Hänsch in recognition for work that he did at the end of the 1990s at the Max Planck Institute in Garching, near Munich, Germany.

He developed an optical "frequency comb synthesiser", which makes it possible, for the first time, to measure with extreme precision the number of light oscillations per second.

By precisely determining its spectral line, scientists were able to draw conclusions about how valid our fundamental physical constants are – if, for example, they change slowly with time.

By the end of the 1980s, the laser spectroscopy of hydrogen had reached the maximum precision allowed by interferometric measurements of optical wavelengths.

When the frequency of a particular radiation is determined, it can be compared to the extremely acute comb spectral lines, until one is found that "fits".

Since 2002, the company Menlo Systems, in whose foundation the Max Planck Institute in Garching played a role, has been delivering commercial frequency comb synthesizers to laboratories all over the world.