On the limits of spin-exchange optical pumping of 3He

Abstract

We have obtained improvement in the 3 He polarization achievable by spin-exchange optical pumping (SEOP). These results were primarily obtained in large neutron spin filter cells using diode bar lasers spectrally narrowed with chirped volume holographic gratings. As compared to our past results with lasers narrowed with diffraction gratings, we have observed between 5% and 11% fractional increase in the 3 He polarization P He . We also report a comparable improvement in P He for two small cells, for which we would not have expected an increase from improved laser performance. In particular, prior extensive studies had indicated that the alkali-metal polarization was within 3% of unity in one of these cells. These results have impact on understanding the maximum P He achievable by SEOP, whether the origin of the improvement is from increased alkali-metal polarization or decreased temperature-dependent relaxation. We conclude that the most likely explanation for the improvement in P He is increased alkali-metal polarization. We have observed P He of between 0.80 and 0.85 in several large cells, which marks a new precedent for the polarization achievable by SEOP. V C 2014 AIP Publishing LLC. [http://dx.

Development of high-performance alkali-hybrid polarizedHe3targets for electron scattering

“…For the few cases where the volume-averaged alkali polarization was much less than the line-averaged alkali polarization ( P A /P A < 0.9), the line-averaged alkali polarization from experiment was, with large uncertainties, systematically lower than those calculated from the model. We further note that a new study [50] seems to indicate that the EPR technique for measuring line-averaged alkali polarizations overestimates the true volume-averaged alkali polarization [52]. More rigorous tests of our simulation under a more diverse set of operating conditions are necessary.…”

Spin echo small angle neutron scattering using a continuously pumped 3He neutron polarisation analyser

“…Additional modifications could be performed to the 3 He analyser such as using a vertical magnetic field [45], which would have the added advantage of removing the need to have mirrors in the beam and would allow the device to be placed closer to the sample, further increasing the angular acceptance. Also the angular acceptance can be further scaled up by the use of larger cells and/or narrower, higher-power lasers [46].…”

An ultra-compact in-situ3He polarizer for high Q-range SANS: on-beam test and future upgrades

“…Formerly diode array bars (DAB) with external cavities using Littrow-type configuration were used [10] as narrow-band optical pumping light has been shown to provide the best SEOP performance. However, it was found later that a new compact method using chirped volume Bragg gratings, CVBG, provides a higher absolute 3 He polarization [11]. Additionally, CVBG narrowed lasers give higher laser intensity output for laser diodes of the same power, and contain much fewer optical elements making the cavity more compact, stable and robust for long term operations required for in-situ 3 He polarizer applications.…”