Berlin 2001 – wissenschaftliches Programm
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A: Atomphysik
A 17: Posters Friday (Spectroscopy)
A 17.58: Poster
Freitag, 6. April 2001, 12:30–15:00, AT3
Spectral characterisation of 1083 nm lasers for optical pumping of helium — •Emmanuel Courtade and Pierre-Jean Nacher — Laboratoire Kastler-Brossel, 24 rue Lhomond, 75005 Paris - France.
Highly polarised 3He gas can be used for several applications such as the realisation of polarised targets for nuclear physics and neutron spin filters, or MRI of human lungs. The most efficient polarisation method relies on metastability exchange optical pumping (ME-OP) using the 23S - 23P atomic transition line at 1083 nm. The absorption profile due to velocity distribution of atoms in a gas at room temperature imposes a matched laser spectral distribution (over 2 GHz) in order not to saturate the 23S - 23P transition and to excite a large number of atoms.
We report on a study of the different laser sources currently used at 1083 nm : DBR laser diode (with wavelength modulation and power amplification), LNA-Nd laser [1], Yb-doped fiber laser [2]. We have directly studied their spectral characteristics with a measurement bandwidth as large as 30 MHz in order to discriminate between frequency jitter and simultaneous multimode operation. For each laser, the saturation of light absorption by 3He atoms has been measured for various intensities Consequences for the kinetics and performance of ME-OP are discussed using a detailed model and recent experimental results.
[1] Aminoff C.G., Larat C., Leduc M., Rev. Phys. Appl. 24 (1989) 827.
[2] Leduc M., Nacher P.-J., Tastevin G. and E. Courtade, Hyperfine Interaction 127 (2000) 443-449.