Comment on "Optically pumped spin-exchange polarized-electron source"

M. Pirbhai et al. [Phys. Rev. A 88, 060701(R) (2013)] reported a new optically pumped spin-exchange polarized-electron source developed to avoid the limitations of the traditional GaAs-type source and to enable a broader range of experiments. The spin-exchange gaseous source has introduced its own limitations with 650-mW laser power producing only 4 mu A of spin-polarized current with a 24% polarization and a 2-eV energy spread depending markedly on tenuous roles of various buffer gases which we consider are not explained cogently. Spin-related beam experiments over many decades have significant achievements using GaAs spin sources.