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Berlin 2001 – wissenschaftliches Programm

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Q: Quantenoptik

Q 35: Laser Spectroscopy

Q 35.5: Vortrag

Freitag, 6. April 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 1S03P1-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)

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