Observation of optical nutation in a collinear fast-ion-beam-laser experiment

We report the first observation of optical nutation in a collinear fast-ion-beam-laser experiment. 35-keV ${\mathrm{Ba}}^{+}$ ions are suddenly tuned into resonance with a strong laser field by post acceleration over a short distance. The degree of excitation as a function of time is monitored by observing the spontaneously emitted light along the ion beam. Oscillations as a function of transition, laser intensity, and laser frequency detuning have been studied. Theoretical curves have been calculated in the density-matrix formalism.