Velocity selection in a Doppler-broadened ensemble of atoms interacting with a monochromatic laser beam

Abstract

There is extensive use of monochromatic lasers to select atoms with a narrow range of velocities in many atomic physics experiments. For the commonplace situation of the inhomogeneous Doppler-broadened (Gaussian) linewidth exceeding the homogeneous (Lorentzian) natural linewidth by typically two orders of magnitude, a substantial narrowing of the velocity class of atoms interacting with the light can be achieved. However, this is not always the case, and here we show that for a certain parameter regime there is essentially no selection – all of the atoms interact with the light in accordance with the velocity probability density. An explanation of this effect is provided, emphasizing the importance of the long tail of the constituent Lorentzian distribution in a Voigt profile.

Keywords:

• Laser spectroscopy
• velocity selection
• Doppler broadening
• Voigt profile

Acknowledgements

The author wishes to thank Aidan Arnold and Lee Weller for illuminating discussions; James Keaveney for assistance with the figures; and James Keaveney and Renju Mathew for a careful reading of the manuscript. On a personal note the author would like to pay tribute to the late Prof. Danny Segal, who provided great enthusiasm for the field of ion trapping and cooling and laser spectroscopy. The author discussed the topic of this paper with Danny at a Summer School in Wales, and will always value the encouragement and support that he received from him at various stages in his career. The author benefited from interactions with Danny in different supervisory and pastoral roles, duties he discharged with grace and humour.

Notes

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the EPSRC [grant number EP/L023024/1]. The data presented in this paper are available for download from [https://doi.org/10.15128/r2rv042t058].