Quantum-beat free-induction decay inTm2+:SrF2: Fourier-transform ESR spectroscopy by optical means

We demonstrate, for the first time, a nanosecond Fourier-transform ESR experiment in solids achieved by optical means. ESR free-induction-decay signals in 0-100 Oe have been observed in the ground state of ${\mathrm{Tm}}^{2+}$:Sr${\mathrm{F}}_2$ as a new type of quantum beat generated by an optical excitation to the absorption band with a circularly polarized light pulse. The Fourier transform of the observed signals gives the ESR spectrum, and the origin of the decay is attributed to the superhyperfine interaction between the ${\mathrm{Tm}}^{2+}$ ion and neighboring fluorine nuclei.