Europhys. Lett.
Volume 76, Number 3, November 2006
Page(s) 409 - 415
Section Electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics
Published online 29 September 2006
Europhys. Lett., 76 (3), pp. 409-415 (2006)
DOI: 10.1209/epl/i2006-10284-4

Helium $2\,^3S$-$2\,^1S$ metrology at $1.557\ \mu {\rm m}$

K. A. H. van Leeuwen1, 2 and W. Vassen1

1  Laser Centre Vrije Universiteit - De Boelelaan 1081 1081 HV Amsterdam, The Netherlands
2  Department of Applied Physics, Eindhoven University of Technology P.O. Box 513, 5600 MB Eindhoven, The Netherlands

received 7 July 2006; accepted in final form 8 September 2006
published online 29 September 2006

An experiment is proposed to excite the "forbidden" $1s2s\,^3S_1$ - $1s2s\,^1S_0$ magnetic dipole (M1) transition at $1.557\ {\rm\mu m}$ in a collimated and slow atomic beam of metastable helium atoms. It is demonstrated that an excitation rate of $5000\ { \rm s^{-1}}$ can be realised with the beam of a 2 W narrow-band telecom fiber laser intersecting the atomic beam perpendicularly. A Doppler-limited sub-MHz spectroscopic linewidth is anticipated. Doppler-free excitation of 2% of trapped and cooled atoms may be realised in a one-dimensional optical-lattice geometry, using the 2 W laser both for trapping and spectroscopy. The very small (8 Hz) natural linewidth of this transition presents an opportunity for accurate tests

of atomic structure calculations of the helium atom. A measurement of the 3He-4He isotope shift allows for accurate determination of the difference in nuclear charge radius of both isotopes.

42.50.Xa - Optical tests of quantum theory.
31.30.Jv - Relativistic and quantum electrodynamic effects in atoms and molecules.
32.80.-t - Photon interactions with atoms.

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