Eur. Phys. J. D 60, 243-256 (2010)
https://doi.org/10.1140/epjd/e2010-00249-6

Optical frequency measurement of the 1S–3S two-photon transition in hydrogen

Laboratoire Kastler Brossel, École Normale Supérieure, CNRS, Université P. et M. Curie - Paris 6, Case 74, 4 place Jussieu, 75252 Paris Cedex 05, France

Corresponding author: ^a biraben@spectro.jussieu.fr

Received: 15 April 2010
Revised: 26 July 2010
Published online: 28 September 2010

Abstract

This article reports the first optical frequency measurement of the 1S–3S transition in hydrogen. The excitation of this transition occurs at a wavelength of 205 nm which is obtained with two frequency doubling stages of a titanium sapphire laser at 820 nm. Its frequency is measured with an optical frequency comb. The second-order Doppler effect is evaluated from the observation of the motional Stark effect due to a transverse magnetic field perpendicular to the atomic beam. The measured value of the (F = 1)-3S_1/2(F = 1) frequency splitting is 2 922 742 936.729(13) MHz with a relative uncertainty of 4.5 × 10^-12. After the measurement of the 1S–2S frequency, this result is the most precise of the optical frequencies in hydrogen.