Optical nutation at a Raman-active transition

Optical nutation at the Raman-active transition 6P(1/2)-6P(3/2) of thallium atoms (omega(R)/2 pi c=7793 cm(-1)) under resonant Raman excitation by a b iharmonic picosecond pulsed field, giving rise to substantial motion of the population, is detected. Optical nutation appears as an oscillatory behavi or of the energy of the anti-Stokes scattering of probe pulses, which follo w with a fixed delay, as a function of the product of the energies of the e xcitation pulses. As a result of the dynamic Stark effect, which decreases the frequency of the transition under study, resonance excitation condition s are satisfied for negative initial detunings of the Raman excitation freq uency from resonance. The Raman scattering cross section for the transition under study is estimated by comparing the experimental data with the calcu lations. (C) 1999 American Institute of Physics. [S0021-3640(99)00213-3].