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 biharmonic picosecond pulsed field, giving rise to substantial motion of the population, is detected. Optical nutation appears as an oscillatory behavior of the energy of the anti-Stokes scattering of probe pulses, which follow with a fixed delay, as a function of the product of the energies of the excitation pulses. As a result of the dynamic Stark effect, which decreases the frequency of the transition under study, resonance excitation conditions are satisfied for negative initial detunings of the Raman excitation frequency from resonance. The Raman scattering cross section for the transition under study is estimated by comparing the experimental data with the calculations. (C) 1999 American Institute of Physics. [S0021-3640(99)00213-3].