EGAS41 - Swansea University

41 st EGAS CP 133 Gdańsk 2009
Femtotesla atomic sensitivity with paraffin-coated Cs cells
N. Castagna 1,∗ , G. Bison 2 , A. Hofer 1 , M. Kasprzak 1 ,
P. Knowles 1 , C. Macchione 1 , A. Weis 1
1 Department of Physics, University of Fribourg,
Chemin du Musée 3, CH–1700 Fribourg, Switzerland
2 Klinik für Neurologie, Universitätsklinikums Jena,
Erlanger Allee 101, D–07747 Jena, Germany
∗ Corresponding author: natascia.castagna@unifr.ch,
We present the latest results from our systematic study of more than 250 nominally
identical alkali atom vapor cells produced by us. The room-temperature cells confine
Cs vapor in evacuated, 28 mm inner diameter paraffin-coated Pyrex bulbs. We have
developed an automated testing facility [1] for characterizing the cell performance. Each
cell is mounted in a standard M x magnetometer configuration [2] based on optically
detected magnetic resonance with circularly polarized D 1 pumping on the F=4 → F=3
transition. Signal amplitude and linewidths are inferred from in-phase and quadrature
magnetic resonance signals. For each cell, we determine the intrinsic (i.e., extrapolated
to zero light and zero rf power) longitudinal, Γ 01 , and transverse, Γ 02 , relaxation rates,
as well as the power dependence of the widths and amplitudes. Our best cell shows
Γ 01 /2π ≈ 0.5 Hz, and Γ 02 /2π ≈ 2 Hz. We find a linear correlation between both relaxation
rates which we explain in terms of reservoir and spin exchange relaxation. For each cell we
have determined the optimal combination of rf and laser powers which yield the highest
sensitivity to magnetic field changes. Out of all produced cells, 94% are found to have
magnetometric sensitivities in the range of 9 to 30 fT/ √ Hz (in the shot-noise limit). We
currently use those cells in a 25-sensor magnetometer array to register dynamic magnetic
field maps of the human heart (see poster by M. Kasprzak et al.).
Figure 1: Histogram of the intrinsic magnetometric sensitivities of 241 cells.
Acknowledgment
Work funded by the Swiss National Science Foundation, #200020–119820, and the Velux Foundation.
References
[1] N. Castagna, G. Bison, G. Di Domenico, A. Hofer, P. Knowles, C. Macchione, H. Saudan,
A. Weis, Applied Physics B, DOI 10.1007/s00340-009-3464-5, (2009)
[2] S. Groeger, G. Bison, J.-L. Schenker, R. Wynands, A. Weis, Eur. Phys. J. D 38, 239
(2006)
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