Theodor W. Hänsch held his Nobel Lecture December 8, 2005, at Aula Magna, Stockholm University. He was presented by Professor Sune Svanberg, Chairman of the Nobel Committee for Physics.

Summary: Development of the frequency comb technique, which allows very high resolution of optical frequencies, began in the 1970s. A breakthrough came in 1999 with a laser-based optical frequency comb synthesizer, which has a very high uniformity. This allowed the accuracy of clocks to improve markedly; from about one second per day in the year 1800 to about one picosecond per day in 2000. A review is given here of the applications of improved atomic clocks.

Theodor W. Hänsch held his Nobel Lecture December 8, 2005, at Aula Magna, Stockholm University. He was presented by Professor Sune Svanberg, Chairman of the Nobel Committee for Physics.