Berlin 2001 – wissenschaftliches Programm
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A: Atomphysik
A 17: Posters Friday (Spectroscopy)
A 17.38: Poster
Freitag, 6. April 2001, 12:30–15:00, AT3
High-frequency No-dqdark stateNo-dq resonances in rare-earth atoms — •Kolachevsky N.N.1, Papchenko A.A.1, Sorokin V.N.1, Akimov A.V.1, and Kanorsky S.I.1,2 — 1P.N. Lebedev Physics Institute, Leninsky prosp., 53, Moscow, 117924 RUSSIA — 2Max-Plank Institute fuer Quantenoptik, Hans-Kopfermann Str.-1, Garching, Germany
It is well-known [1], that the theoretical limit for the width of No-dqdark stateNo-dq resonance in a Λ - system is defined by the relaxation time of the atomic coherence between lower levels and does not depend on the width of the upper level. It was shown experimentally [2], that the width of a No-dqdark stateNo-dq resonance can reach tens of Hertz in Cs atomic vapor. The atomic system in such coherent state can be considered as a high-quality secondary frequency standard with a stabilized difference of two optical frequencies.
The fine structure components of 4f n6s2 ground multiplet in rare-earth elements have a typical splitting of 10-100 THz which far exceeds the hyperfine splitting of ground state of alkali atoms (∼10 GHz). These levels in rare-earths are shielded by the outer closed 6s2 shell, so the collisional relaxation cross-section of the fine-structure components is smaller than the hard-sphere cross section [3]. If two optical frequencies (ω1 , ω2) are applied to the rare-earth atom as to build the coherence between the fine-structure components, one would observe narrow coherent population trapping resonances on a high deferred frequency Δω12 = ω1 - ω2. which can lay even in optical range (e.g. 2πc/Δω12 = 1.14 µm for the ground state 4f 136s2(2Fo7/2) and 4f 136s2(2Fo5/2) term in Tm atom). The Q-factor of No-dqdark stateNo-dq resonances in this case may be increased for 2-3 orders of magnitude in comparison with alkali atoms due to the high carrier frequency Δω12.
A Samarium atom with a precisely known level structure [4] was taken for our experiments. In Sm the first metastable level 4f 66s2(7F1) is separated from the ground state 4f 66s2(7F0) by 8.79 THz. We chose these two levels as the lower levels of Λ - system while the upper level was 4f 6(7F)6s6p(3Po) 9Fo1.
Two ECDLs (672 nm, 686 nm) were tuned to the corresponding transitions in 154Sm. The coherent population trapping effect was studied in co-propagating beams configuration with the lasers locked to the stable interferometer. We recorded absorption spectra under different conditions: varying external magnetic fields and buffer gas pressure. No-dqDarkNo-dq resonances were observed on the broad contour of induced absorption caused by velocity collisional changes. Hard sphere collisional model gave an appropriate results in frames of our experiment configuration.
We demonstrated the perspectives of the approach aimed in shifting the measurements in high-frequency region. Having a stable oscillator at Δω12 frequency [5], one would be able to lock two optical fields phase-coherently and exclude the effect of mutual phase fluctuations from the resonance contour.
Acknowledgments. The work is supported by Volkswagen Stiftung I/73 647 and the Program of the Russian Ministry of Science No-dqPhysics of quantum and wave processesNo-dq.
[1] E. Arimondo, Progress in Optics XXXV 257 (1996).
[2] R. Wynands, A. Nagel, Appl.Phys. B 68 1 (1999).
[3] E. Buhr, J. Mlynek, Phys.Rev.A 36 (6) 2684 (1987).
[4] N. Kolachevsky et al. Quantum Electronics 90(2) 49 (2001).
[5] J. Reichert et al., Phys.Rev.Lett. 84 3232 (2000).