Professor Christopher Foot

Abstract:

CW Doppler-free two-photon spectroscopy was used to measure the 1S-2S transition frequency in atomic hydrogen gas with a precision of six parts in 10**1**0. The result for the energy level separation is f(1S-2S) equals 2 466 061 413. 8 (1. 5) MHz and can be used to extract a value of the 1S Lamb shift. Choosing a value of the Rydberg constant measured independently by high-resolution spectroscopy of the hydrogen Balmer- beta transition, a value of DELTA f//L//a//m//b(1S) equals 8 173. 3 (1. 7) MHz was obtained, in good agreement with the theoretical prediction of 8 173. 06 (20) MHz. The experimental result can be interpreted as a measurement of the Rydberg constant. A value of R// infinity equals 109 737. 315 (7) cm** minus **1 was obtained, in agreement with recent precise measurements.

Abstract:

The hydrogen atom is an important testing ground for fundamental physical theory, because it is the simplest stable atomic system and its properties can be calculated to enormous precision. Measurements on hydrogen played a major role in the development of quantum electrodynamics (QED), a theory of electromagnetic interactions which includes quantization of the radiation field1,2. Tests of QED in hydrogen involve precision measurements of transition frequencies; the transition generally studied is between two excited states (2s2S1/2 and 2p2P1/2). Much higher precision is possible if a transition involving the ground state is studied, but this potential has not so far been exploited because of experimental difficulties. We have now carried out an experiment of this type which has given preliminary results and opens new possibilities for precision tests of QED in the future. © 1987 Nature Publishing Group.