Europhys. Lett.
Volume 61, Number 2, January 2003
Page(s) 181 - 186
Section Nuclear physics
Published online 01 January 2003
DOI: 10.1209/epl/i2003-00210-x
Europhys. Lett., 61 (2) , pp. 181-186 (2003)

Nuclear laser spectroscopy of the 3.5 $\un{eV}$ transition in $\chem{Th}$-229

E. Peik and Chr. Tamm

Physikalisch-Technische Bundesanstalt - Bundesallee 100 38116 Braunschweig, Germany

(Received 17 June 2002; accepted in final form 11 November 2002)

We propose high-resolution laser spectroscopy of the 3.5 $\un{eV}$ nuclear transition in $\chem{Th}$-229 in isolated atoms. Laser excitation of the nucleus can be detected efficiently in a double-resonance method by probing the hyperfine structure of a transition in the electron shell. It is shown that for a suitably chosen electronic level, the frequency of the nuclear transition is independent of external magnetic fields to first order and of electric fields to second order. This makes $\chem{Th}$-229 a possible reference for an optical clock of very high accuracy. The nuclear-electronic double-resonance method can be conveniently applied to a laser-cooled ion of $\chem{^{229}Th^{3+}}$ in a radiofrequency trap. Further applications of nuclear laser spectroscopy are discussed.

23.20.-g - Electromagnetic transitions.
42.62.Fi - Laser spectroscopy.
33.40.+f - Multiple resonances (including double and higher-order resonance processes, such as double nuclear magnetic resonance, electron double resonance, and microwave optical double resonance).

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