A Miniature Permanent Magnet Assembly with Localized and Uniform Field with an Application to Optical Pumping of Helium

Atomic state preparation can benefit from a compact and uniform magnetic field source. Simulations and experimental measurements have been used to design, build, and test such a source and then apply it to the optical pumping of atomic helium. This source is a 9.5 mm (3/8″) OD × 6.7 mm (1/4″) ID × 9.5 mm (3/8″) long, NdFeB-N42 assembly of 1.6 mm (1/16″) thick customized annular magnets. It has octupole decay with a residual dipole far field from imperfect dipole cancelations. Fast B-field decay localizes the field, minimizing the need for shielding in applications. It has a greater than 50% clear aperture with a uniform and collimated magnetic field consistent with the prediction of several models. The device is applied to a high precision 3,4He laser spectroscopy experiment using σ+ or σ− optical pumping currently resulting in a measured 99.3% preparation efficiency and in accordance with a rate equation model.

A Miniature Permanent Magnet Assembly with Localized and Uniform Field with an Application to Optical Pumping of Helium

Atomic state preparation can benefit from a compact and uniform magnetic field source. Simulations and experimental measurements have been used to design, build, and test such a source as shown by optical pumping of atomic Helium. This source is a 9.5 mm (3/8") OD x 6.7 mm (1/4") ID x 9.5 mm (3/8") long, NdFeB-N42 assembly of 1.6 mm (1/16") thick customized annular magnets. It has octopole decay with a residual dipole far field from imperfect dipole cancelations. It has greater than 50% clear aperture with uniform and collimated magnetic field consistent with the prediction of several models. Octopole roll-off localizes the field minimizing the need for shielding in applications. The device is applied to a high precision 3,4He laser spectroscopy experiment using σ+ or σ- optical pumping currently resulting in a measured 99.3% preparation efficiency and in accordance with a rate-equation model.

Precision spectroscopy of atomic helium

Helium is a prototype three-body system and has long been a model system for developing quantum mechanics theory and computational methods. The fine-structure splitting in the 23P state of helium is considered to be the most suitable for determining the fine-structure constant α in atoms. After more than 50 years of efforts by many theorists and experimentalists, we are now working toward a determination of α with an accuracy of a few parts per billion, which can be compared to the results obtained by entirely different methods to verify the self-consistency of quantum electrodynamics. Moreover, the precision spectroscopy of helium allows determination of the nuclear charge radius, and it is expected to help resolve the ‘proton radius puzzle’. In this review, we introduce the latest developments in the precision spectroscopy of the helium atom, especially the discrepancies among theoretical and experimental results, and give an outlook on future progress.

Development of a Thulium Fiber Laser for an Atomic Spectroscopy Experiment

A convenient thulium fiber laser source is described with 3 W of output power operating at a wavelength of 2059 nm with a slope efficiency of 49% with respect to input pump power and 60% with respect to absorbed pump power. The laser was applied in an atomic helium spectroscopy experiment to quench 3He (2058.63 nm) and 4He (2058.69 nm) meta-stable singlets (21S0), allowing for further investigation of the helium fine structure. The customized laser effectively eliminates the singlet counts to well below a background level (1%). A simplified analysis describes the basic laser performance with fitted constants in reasonable agreement with previous work.