Electric-field ionisation of laser-excited Rydberg atoms in a magnetic field

A weak magnetic field has been found to have a pronounced effect on the selective field ionisation (SFI) of Rydberg atoms. Field ionisation quantum beats have been observed from coherently excited sodium 30d²D _3/2 Zeeman levels. Both pi laser excitation and SFI took place in a magnetic field of approximately 0.3 G. The time evolution of the Zeeman levels leads to the observation of SFI traces that range between those seen for pi and sigma laser excitation in zero magnetic field. Good agreement is found between theory and experiment, except for the depth of modulation of the quantum beats, which is less than the theoretical value.