Laser-induced phonon-phonon interactions in bismuth

We compute laser-induced interactions between coherent phonons in bismuth and demonstrate that they are key to understanding important experiments performed with intense femtosecond laser pulses. In particular, we find mixing signals and higher harmonics arising from the coupling between phonons of different and the same symmetries, respectively. We show that the phonon-phonon interaction is strongly dependent on the laser fluence and is for that reason only observable when sufficiently strong laser pulses are used. Our results offer a unified description of the different experimental observations performed so far on bismuth.