A broadband Ytterbium-doped tunable fiber laser for 3He optical pumping at 1083 nm

摘要

Large amounts of hyperpolarized 3He gas with high nuclear polarization ratesare required for use in neutron spin filters or nuclear magnetic resonanceimaging of human lung. Very high efficiency can be obtained by metastabilityexchange optical pumping using multimode lasers to excite the 23S-23Ptransition at 1083 nm. Broadband Ytterbium-doped tunable fiber lasers have beendesigned for that particular application. Different options for thearchitecture of the fiber oscillator are presented and compared. Emphasis isgiven to a linear cavity configuration that includes a high reflectivity fibermirror and a low reflectivity tunable fiber Bragg grating. Optical measurementsare performed to finely characterize the spectral behavior of the lasers.Atomic response is also quantitatively probed to assess the optimal design ofthe oscillator for optical pumping. Multimode operation matching the 2 GHzDoppler-broadened helium resonance line and tunability over more than 200 GHzare demonstrated. Boosting the output of this fiber laser with a Yb-doped fiberpower amplifier, all-fiber devices are built to provide robust, high powerturn-key sources at 1083 nm for improved production of laser polarized 3He.