Measuring the Frequency of Light with Mode-Locked Lasers

  • Thomas Udem
  • Jörg Reichert
  • Ronald Holzwarth
  • Markus Niering
  • Martin Weitz
  • Theodor W. Hänsch
Part of the Topics in Applied Physics book series (TAP, volume 79)


We have used the comb of optical frequencies emitted by a mode-locked laser as a ruler to measure frequency differences of up to 45.2 THz between two laser signals. We have shown that the modes are distributed uniformly in frequency space within the experimental limit of 3.0 parts in 1017, and that the mode separation equals the pulse repetition rate within an experimental limit of 6.0 parts in 1016. We have used this comb to bridge a frequency mismatch of 18.4 THz for an absolute optical frequency measurement of the cesium D 1 line at 335 THz (895 nm) by comparison with the fourth harmonic of a methane-stabilized He-Ne Laser at 88.4THz (3.39 m). Bridging a frequency gap of 45.2THz, we could demonstrate for the first time a new type of frequency chain that is based on the measurement of frequency differences between laser harmonics. With this type of apparatus we have also measured the absolute frequency of the hydrogen 1S 2S transition at 2466 THz (121 nm) in a direct comparison with the output signal from a commercial cesium atomic clock.


Pulse Repetition Rate Optical Frequency Free Spectral Range Frequency Comb Gate Time 
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Copyright information

© Springer-Verlag Berlin Heidelberg 2001

Authors and Affiliations

  • Thomas Udem
    • 1
  • Jörg Reichert
    • 1
  • Ronald Holzwarth
    • 1
  • Markus Niering
    • 1
  • Martin Weitz
    • 1
  • Theodor W. Hänsch
    • 1
  1. 1.Max-Planck-Institut für QuantenoptikGarchingGermany

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