Time-resolved non-linear spectroscopy of local/non-local biphonon interaction in NH4Cl

Abstract The interaction of the 2 v 4 biphonon with the corresponding overtone of the 15 N impurities in natural ammonium chloride is investigated by a time-resolved coherent picosecond technique. The observation of quantum beats evidences the splitting of the quasi-biphonon into two quasi-bound states of very close frequencies and comparable Raman intensities. The spectral and dynamical features of this doublet are measured as a function of temperature. The results indicate the important role played by the two-phonon continuum in the formation and in the coherent decay of these states.