Theodor W. Hänsch

Theodor W. Hänsch is a German physicist whose precision laser spectroscopy and optical frequency comb techniques transformed the measurement of atomic frequencies. He shared the 2005 Nobel Prize in Physics.

Laser spectroscopy: The study of matter through its interaction with laser light. It is the broad experimental field in which Hänsch developed precision methods.
Optical frequency comb: A laser spectrum consisting of evenly spaced, phase-coherent optical frequencies. Hänsch helped develop the comb technique that links optical frequencies to measurable radio frequencies.
Optical atomic clock: A clock that uses an optical-frequency transition in atoms or ions as its reference. Frequency combs compare its rapid optical oscillations with countable electronic frequencies.
John L. Hall: An American physicist who developed precision laser spectroscopy and shared the 2005 Nobel Prize in Physics. Hall shared the Nobel Prize with Hänsch for contributions to precision laser-based spectroscopy.
Frequency comb: A set of equally spaced, phase-coherent frequencies generated by a periodic signal. The optical frequency comb became a broadly used measurement tool beyond Hänsch’s original experiments.
Optical frequency: The number of oscillations per second of electromagnetic radiation in the visible or nearby spectral range. Measuring optical frequencies with exceptional precision became a central aim of his research.
Mode-locked laser: A laser that emits a regular train of short pulses by locking the phases of its longitudinal modes. Its pulse train produces the evenly spaced spectral modes used in frequency-comb measurements.
Hydrogen spectroscopy: The measurement of light emitted or absorbed by hydrogen atoms to determine their energy levels. Hänsch’s precision measurements of hydrogen tested quantum electrodynamics and fundamental constants.
Roy J. Glauber: An American theoretical physicist awarded half of the 2005 Nobel Prize in Physics for quantum optics. Glauber received the other half of the prize shared by Hänsch and Hall.
Precision measurement: The experimental determination of physical quantities with tightly controlled uncertainty. Hänsch’s methods expanded precision measurement into optical frequencies.

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