Spin dynamics of dense alkali-metal atoms

The free induction signals of dense Rb atoms are observed with an injection-seeded power laser diode. The decay rate of signals is found to depend on the number density of Rb atoms, the static magnetic field, the electron spin polarization, and the pulse area of the oscillating magnetic field. We note that the observed broadening of the magnetic resonance line, appearing at high polarization and large pulse area, is the key to understanding the spin dynamics of the precessing atoms which interact with each other. The feature of broadening is quantitatively interpreted by numerically calculating, in a wide range of parameters, the nonlinear Liouville equation that includes the spin-exchange interaction between Rb atoms.