Nuclear Dynamic Polarization by Optical Electronic Saturation and Optical Pumping in Semiconductors

A nonresonant Overhauser effect by photoexcited conduction electrons is obtained on ${\mathrm{Si}}^{29}$ nuclei in silicon at 77°K in two different ways: (a) Saturation of the electronic magnetization is achieved with unpolarized light by exciting an equal number of spins up and spins down. (b) Polarized electronic spins are produced by optical pumping with circularly polarized light; the nuclear magnetization obtained in 1 G by optically pumped electrons corresponds to the equilibrium value at 77°K in 28 kG.