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Q: Quantenoptik
Q 35: Laser Spectroscopy
Q 35.5: Talk
Friday, April 6, 2001, 16:45–17:00, H 2013
Towards the Quantum Projection Noise Limit in an Optical Ca-Frequency Standard — •Guido Wilpers, Tomas Binnewies, Uwe Sterr, Jürgen Helmcke, and Fritz Riehle — Physikalisch–Technische Bundesanstalt, Bundesallee 100, D–38116 Braunschweig
A high–accuracy optical frequency standard is realised by
using an atom-light-interferometer in the time-domain probing the 657 nm
1S0→3P1-transition of 40Ca-atoms
laser-cooled to ca.
3 mK. Currently, the achievable relative uncertainty is
4 × 10−14. The short-term stability is limited by the
detection scheme that measures the fluorescence of the excited atoms
with a probability of only 10−3. To improve the short-term
stability
of the standard we have investigated two different methods for detecting
the
excited atoms with a probability close to unity and hence, the possibility
to
reach the limit imposed by the quantum projection noise.
One method uses a shelving technique [1] based on the 423 nm
cooling transition (4s2 1S0→ 4s4p 1P1) that
can
scatter up to 108
photons/s from the ground state. Probing the ground state allows one to
make use of
the cooling laser, but cooled atoms that do not take part in the excitation
on the narrow
transition (about 80 %) give rise to a background. The second method uses
the 430 nm
4s4p 3P1→4p2 3P0 transition that can scatter
107 photons/s from the excited state of the clock transition.
This scheme probes the excited state free of background at the expense of
an additional laser.
Supported by the DFG under SFB 407.
[1] C. W. Oates et al, Eur. Phys. J. D 7, 449 (1999)