Energy Shifts of the Magnetic Sublevels ofS13Helium Caused by Optical Pumping

It has been observed experimentally that the energy spacing between the magnetic sublevels of the $2{}_{}{}^3{}_{}{}^{}S_1^{}{}_{}{}^{}$ state of helium as detected by optical pumping varies with the intensity and character of the resonant radiation. The relative shift as a function of the intensity, polarization, and spectral distribution are observed and measured. The energy shifts are on the order of 50-60 cps and become smaller as the intensity of the light decreases. A second lamp containing ${\mathrm{He}}^3$ incident on the absorption cell in the same manner as the pumping lamp also produces an energy shift. An explanation of the light shift in metastable helium is discussed.