Light narrowing of rubidium magnetic-resonance lines in high-pressure optical-pumping cells

We report on some unusual magnetic-resonance phenomena of optically pumped Rb vapor in high-pressure gas cells. When Rb-Rb spin exchange is the fastest spin-relaxation rate, we observe a considerable narrowing of the magnetic-resonance linewidths with increasing pump-laser power. The experimentally measured Rb magnetic-resonance linewidths are in excellent agreement with a theoretical model, which includes the processes of Rb-He and Rb-Xe spin destruction, Rb-Rb spin exchange, and Rb optical pumping.