MULTIPHOTON ABSORPTION AND PHASE CORRELATION BETWEEN DRIVING FIELD AND MOLECULAR DIPOLE

We study by numerical simulation two important effects in the mechanis m of multiphoton exchange between a diatomic molecule and an intense l aser field: the dephasing and rephasing of the molecular dipole with r espect to the driving field and the loss of coherence of the molecular wavepacket due to anharmonicity. We restrict the analysis to times of the order of the first recurrence period of the process and to the ca se where few photons are absorbed. We take the example of the HF molec ule as a representative case. We find that a representation of the ind uced dipole by a simple waveform is useful for predicting the differen t scenarios that can occur. In particular, we focus on a 'throttling' phenomenon due to anharmonicity of the vibrations or to rotational mot ion.