Optically Induced Precessing Magnetization in Ruby near the Level Anticrossing Points in ⁴A₂

Using excitation by ultrashort light pulses from a mode-locked ruby laser, we have observed optically induced magnetization precessing at a frequency corresponding to the energy separation near the level anticrossing points of the ground state ⁴A₂ in ruby at room temperature. The motion of the magnetization is detected by a pick-up coil. The decay time of the signal is 5~6 ns. The analysis is made by using the model of fictitious spin 1/2 and the agreement with the experiment is satisfactory.