Polarisation of a spin-frac(1, 2) β-NMR probe ¹¹Be using collinear laser optical pumping

Spin frac(1, 2) probes have special importance in the field of NMR, since they have no electric quadrupole moment and are thus pure magnetic sensors. The absence of quadrupolar splittings greatly simplifies the NMR frequency spectrum. That the muon is spin frac(1, 2) is one of the reasons it has become so useful as a magnetic probe. Until now there has been no spin frac(1, 2) probe suitable for beta-detected NMR. Such a probe would be particularly useful in complex materials, which are in general non-cubic. In this paper we describe the development of a low energy beam of spin-polarised ¹¹Be, which is the lightest spin frac(1, 2) isotope suitable for β-NMR. The intensity of the ¹¹Be⁺ beam-generated by a laser ionisation source-is about 10⁶ / s. The ¹¹Be nuclei are polarised by collinear laser optical pumping with an externally frequency doubled dye laser tuned to the ²S_{1 / 2}-²P_{1 / 2} transition of ¹¹Be⁺ at 313 nm.