Absolute Optical Frequency Measurement of the Cesium D1 Line with a Mode-Locked Laser

Th. Udem, J. Reichert, R. Holzwarth, and T. W. Hänsch
Phys. Rev. Lett. 82, 3568 – Published 3 May 1999
PDFExport Citation


We have measured the absolute optical frequency of the cesium D1 line at 335 THz (895 nm). This frequency provides an important link for a new determination of the fine structure constant α. The D1 line has been compared with the fourth harmonic of a methane stabilized He-Ne laser at 88.4 THz ( 3.39μm). To measure the frequency mismatch of 18.39 THz between 4×88.4THz=354THz and the D1 line a frequency comb spanning around 244 000 modes of a Kerr-lens mode-locked laser was used. We find 1 167 688 (81) kHz for the hyperfine splitting of the 6P1/2 state and 335 116 048 807 (41) kHz for the hyperfine centroid from which we derive α1=137.0359924(41).

  • Received 17 December 1998


©1999 American Physical Society

Authors & Affiliations

Th. Udem, J. Reichert, R. Holzwarth, and T. W. Hänsch

  • Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, 85748 Garching, Germany

References (Subscription Required)

Click to Expand

Vol. 82, Iss. 18 — 3 May 1999

Reuse & Permissions
Access Options
Heating up of Superconductors
January 27, 2017

This collection marks the 30th anniversary of the discovery of high-temperature superconductors. The papers selected highlight some of the advances that have been made to date, both in understanding why these compounds behave in the way they do, and in utilizing them in applications. The papers included in the collection have been made free to read.

APS and CERN Sign Open Access Agreement for SCOAP3

APS and CERN, the host organization of SCOAP3 (Sponsoring Consortium for Open Access Publishing in Particle Physics), have signed an agreement to make the high-energy physics (HEP) articles published in three leading APS journals open access beginning January 1, 2018. This agreement acts to support the publishing of open access content for wider benefit of the HEP community.

Authorization Required




Sign up to receive regular email alerts from Physical Review Letters

Log In



Article Lookup

Paste a citation or DOI

Enter a citation