Optical induction of magnetization and observation of fast spin dynamics in aqueous solutions of copper ions

Optically induced magnetization and its fast dynamics in aqueous solutions of transition-metal ions is studied by the polarization spectroscopy with the pump-probe technique. The fast spin dynamics in solutions at room temperature, which cannot be detected by the conventional magnetic-resonance methods, was observed by an all-optical method. A circularly polarized pump pulse creates the magnetization in the ground state of the copper ions in aqueous solutions of copper sulfate, and the time evolution of the magnetization in the subnanosecond region is monitored through the change of the polarization of the probe pulse. Quantum-beat free-induction decay signals are observed in transverse magnetic fields, whose Fourier transform gives the ESR spectra. The observed concentration dependence of the relaxation rate in no external magnetic field is interpreted by the spin cross relaxation due to the magnetic dipole interaction between the copper ions.