He was still at school when Theodor Hänsch already knew what he wanted to be: a physics professor.

An assistant to a university professor he knew had helped him calibrate a self-made Geiger-Müller counter.

It was then that he saw for the first time what a laboratory was like and what a professor could afford, he said later.

Originally, Hänsch, who was born in Heidelberg, studied there and received his doctorate in 1969, wanted to become a nuclear physicist.

But then he was fascinated by a light source that was invented in the early 1960s: the laser would not let go of him for the rest of his life.

Manfred Lindinger

Editor in the “Nature and Science” section.

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For Hänsch, the laser was the ideal tool for precision measurements. This special light source enabled him to measure many elementary properties of the hydrogen atom extremely precisely and to compare them with theoretical predictions. The accuracy achieved even amazed some theorists, whose calculations could hardly keep up with the measurement results.

Hänsch acquired the experimental tools in the 1970s and 1980s at Stanford University in Palo Alto from laser pioneer Arthur Schawlow. He was so successful that he got his own professorship at Stanford in 1975. After sixteen years, Hänsch turned his back on the USA and went to Garching, where he was appointed director of the Max Planck Institute for Quantum Optics in 1986 at the age of 45. Almost twenty years later, Theodor Hänsch was awarded the Nobel Prize in Physics in 2005 for the invention of the “frequency comb”. With this laser technology, the rapid oscillations of light beams can be counted and wavelengths can be precisely determined. The invention made it possible to build new, even more precise atomic clocks in which the microwaves of cesium atoms no longer beat the beat,but the much faster optical frequencies of atoms.

Professor for life

A year after his Nobel Prize, Hänsch made headlines again on his sixty-fifth birthday when he protested against his compulsory retirement as part of the civil service law and threatened to emigrate again to America if necessary.

He won and negotiated a regulation with the Free State of Bavaria, according to which he was allowed to hold a chair at the Ludwig Maximilians University for life.

At the MPI in Garching, the emeritus can continue researching in his own laboratory.

In addition to persistence, diligence and the will to work hard, the brilliant physicist, who tends to strike quiet tones and avoids the hype about his person, is said to have a pronounced instinct to play. In Stanford, so a colleague reports, Hänsch had made a small milling machine with which he sharpened his pencils. The highlight: The machine was controlled by the first Commodore computer that was available at the time.

Hänsch's laser experiments with pudding are also legendary.

After directing a laser beam at a drop of water, which suddenly became a laser itself and shone green, the idea occurred to him to try the same with pudding.

He and his colleagues cooked pudding in Stanford for days - with added gelatine, the experiment finally succeeded.

The jelly laser was never actually used.

However, Hänsch and his colleagues were able to show that almost anything was suitable as a laser medium.

Shortly thereafter, the dye laser was invented.

Today Theodor Hänsch celebrates his eightieth birthday.