Optical Excitation of Zeeman Coherence in Ruby

Optically induced Zeeman coherences between various pairs of sublevels in the ground state ⁴A₂ of a sample ruby (0.05 wt.%) were observed at room temperature by using impact excitation with circularly polarized resonant light pulses from a mode-locked ruby laser. The precessing magnetization associated with Zeeman coherence was detected magnetically in UHF, VHF and X-band microwave regions. The observed signals can be regarded as various types of ESR free induction decay signals and the decay times were of the order of nanosecond. Sustained precession signals were also observed. Characteristics of the signals were explained by numerical solutions of the Liouville equation.