Narrow band laser source for efficient 3He polarization
- OptiGrate Corp., Oviedo, FL (United States)
Polarized 3He is widely in polarized neutron scattering as neutron polarizers or analyzers. Increasing 3He polarization can improve both neutron polarization and transmission which are important for any polarized neutron experiments. Here at the US, 3Hee is usually polarized using spin-exchange optical pumping (SEOP), where 3He gains polarization via spin-exchange collisions with laser pumped alkali metals, typically rubidium (Rb) and potassium (K). Over the last two decades, 3He polarization has improved from around 50% to around 80% due to the application of spectral narrowed diode lasers which narrows the laser linewidth from 2 nm to between 0.2 nm and 0.3 nm. However, the highest 3He polarization achieved so far is limited to about 85%. The mechanism behind this is still not well understood, but it is suspected that a laser with an ultra-narrow linewidth and lower broadband background may further improve the 3He polarization. In addition, if we define the spin-exchange efficiency as the ratio of the rate at which the polarized 3He is produced to the rate at which the alkali atom polarization is lost through various collisions, K has much higher spin-exchange efficiency than Rb does. In principle, direct pumping of K should improve both the pumping efficiency and the production rate of polarized 3He. However, because of the small fine structure splitting in K (D1 770 nm, D2 766.7 nm), the laser used to pump K needs to have a ultra-narrow spectrum tuned at 770 nm and minimal broadband background as the pumping of the K D2 transition will reduce the pumping efficiency. Such a laser is not readily available. Therefore, the current practice of polarizing 3He is through a hybrid SEOP method in which the laser tuned at Rb D1 transition (795 nm) polarizes Rb first and then Rb transfers its polarization to K. This hybrid method takes advantages of the more accessible 795 nm laser and gains some pumping efficiency. But to realize the full potential in SEOP, direct pumping of K would be necessary. The new Optigrate laser provides a tool to investigate the impact on the pumping efficiency and achievable 3He polarization under the condition of ultra-narrow spectrum and very low background.
- Research Organization:
- OptiGrate Corp., Oviedo, FL (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- SC0017197
- OSTI ID:
- 1434619
- Report Number(s):
- DOE-OPTIGRATE-17197
- Country of Publication:
- United States
- Language:
- English
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