His interest in science was ignited at an early age by his surroundings. The family lived in the house in Heidelberg that had previously belonged to the chemist Robert Bunsen, and the street was named Bunsenstrasse in his honour. At six years of age, the curious Hänsch asked his father why a street had been named after Bunsen. The next day, his father brought home a Bunsen burner and showed how table salt glows bright yellow in the blue flame. According to Hänsch, “it was obvious to me that I had to find out more about light and atoms.”

Throughout his school years, Hänsch spent all his allowance on chemicals bought from pharmacies and stored them in his parents’ bedroom. However, he moved on to physics and electronics experiments after what he refers to as “an intimidating accident with bomb-making materials.” One of his later projects involved building a Geiger counter to experiment with some radioactive material bought from a paint factory. To calibrate the instrument, he went to the nuclear physics laboratory at the University of Heidelberg, where an assistant helped him. At that moment, Hänsch said he decided to become a physicist and university professor.

Hänsch graduated in physics at the University of Heidelberg, and having developed a fascination with lasers, he began a two-year research diploma that continued into a doctoral thesis, which he completed in 1969. The following year, he took a position as a postdoctoral fellow at Stanford University in the US, working with Arthur Schawlow, the co-inventor of the laser (and who received the 1981 Nobel Prize in Physics).

Under Schawlow’s mentorship, Hänsch created the high-spectral resolution laser — the first laser in which the colour could be changed while maintaining the distinctive wavelengths of each colour to an exceptionally precise degree. Hänsch described it as a simple invention that caused a great deal of excitement: the high-spectral resolution laser provided researchers with a tool for measuring and defining characteristic frequencies of electromagnetic radiation absorbed and emitted by an atom considerably more accurately than other methods.

Looking to develop more precise methods for measuring laser light frequencies, Hänsch came up with the concept for the optical frequency comb technique in the late 1970s. He hypothesized that ultra-short pulses of laser light could create a series of precisely spaced frequency peaks, resembling evenly spaced teeth of a comb, which could act as a form of ruler to separate and measure different frequencies.

While developing the concept, Hänsch returned to Germany in 1986 to take up a position at the University of Munich, and he founded the Division of Laser Spectoscopy at the Max Planck Institute. Between 1997 and 2000, and with the help of John Hall’s research, Hänsch’s optical frequency comb concept evolved into a working model, measuring light frequencies emitted from atoms and molecules to within an unprecedented accuracy of fifteen digits. Such precise frequency measurements for light made it possible to develop highly accurate clocks and improved global positioning system technology, and even to search for changes in fundamental physical constants of the universe over time.

Hänsch has also taught a number of distinguished students over the years, including Carl Wieman, who was awarded the 2001 Nobel Prize in Physics. While at Stanford in the mid-1970s, one of the students in his undergraduate classes was Steve Jobs, who founded Apple Computers, and Hänsch bought one of the first computers produced by the company.

Nobel Prize in Physics 2005
Theodor Hänsch’s Nobel Lecture
Theodor Hänsch’s group at the Max Planck Institute
Wikipedia: Theodor Hänsch