We consider parametric interactions of laser pulses in a coherent macroscopic ensemble of resonant atoms, which are possible in the strong coupling regime of light-matter interaction. The spectrum condensation (lasing at collective vacuum Rabi sidebands) was studied in an active cavity configuration. Parametric interactions under the strong light-matter coupling were proved even in free space. In contrast to bichromatic beats in a cavity, they were shown to appear due to interference between polaritonic wave packets of different group velocities.
@article{arxiv.quant-ph/0607033,
title = {Strong light-matter coupling: parametric interactions in a cavity and free-space},
author = {I. B. Mekhov and V. S. Egorov and V. N. Lebedev and P. V. Moroshkin and I. A. Chekhonin and S. N. Bagayev},
journal= {arXiv preprint arXiv:quant-ph/0607033},
year = {2007}
}