1,892 research outputs found
Prospects for a Nuclear Optical Frequency Standard based on Thorium-229
The 7.6-eV-isomer of Thorium-229 offers the opportunity to perform high
resolution laser spectroscopy of a nuclear transition. We give a brief review
of the investigations of this isomer. The nuclear resonance connecting ground
state and isomer may be used as the reference of an optical clock of very high
accuracy using trapped and laser-cooled thorium ions, or in a compact
solid-state optical frequency standard of high stability.Comment: 5 pages, 1 figure; Proceedings of the 7th Symposium on Frequency
Standards and Metrology, 5-11 October 2008; reference added for section
Frequency comparisons and absolute frequency measurements of 171Yb+ single-ion optical frequency standards
We describe experiments with an optical frequency standard based on a laser
cooled Yb ion confined in a radiofrequency Paul trap. The
electric-quadrupole transition from the ground state to the
state at the wavelength of 436 nm is used as the reference
transition. In order to compare two Yb standards, separate
frequency servo systems are employed to stabilize two probe laser frequencies
to the reference transition line centers of two independently stored ions. The
experimental results indicate a relative instability (Allan standard deviation)
of the optical frequency difference between the two systems of only, so that shifts in the sub-hertz range can be
resolved. Shifts of several hertz are observed if a stationary electric field
gradient is superimposed on the radiofrequency trap field. The absolute optical
transition frequency of Yb at 688 THz was measured with a cesium atomic
clock at two times separated by 2.8 years. A temporal variation of this
frequency can be excluded within a relative uncertainty of yr. Combined with recently published values for the constancy
of other transition frequencies this measurement provides a limit on the
present variability of the fine structure constant at the level of
yr.Comment: 12 pages, 5 figures, Proceedings of MPLP'04, Novosibirsk, August
22.-27., 200
Comparison of two single-ion optical frequency standards at the sub-Hertz level
We describe experimental investigations on an optical frequency standard
based on a laser cooled 171Yb+ ion confined in a radiofrequency Paul trap. The
electric-quadrupole transition from the 2S1/2(F=0) ground state to the
2D3/2(F=2) state at the wavelength of 436 nm is used as the reference
transition. The reference transition is probed by a frequency-doubled,
frequency-stabilized diode laser and is resolved with a Fourier-limited full
halfwidth of approximately 30 Hz. In order to compare two 171Yb+ standards,
separate frequency shift and servo systems are employed to stabilise the probe
frequency to the reference transition line centers of two independently stored
171Yb+ ions. The present experimental results indicate a relative instability
(Allan standard deviation)of the optical frequency difference between
the two systems of sigma_y(1000 s)=1.0E-15 and a mean frequency difference of
0.2 Hz. Shifts in the range of several Hertz are observed in the frequency
difference if a stationary electric field gradient is superimposed on the
radiofrequency trap field. This measurement permits a first experimental
estimate of the electric quadrupole moment of the 2D3/2 state of Yb+.Comment: To appear in "Laser Spectroscopy XVI", eds: P. Hannaford, A. Sidorov,
H. Bachor, and K. Baldwin (World Scientific, Singapore, 2004
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