Coherent amplitudon generation in blue bronze through ultrafast interband quasi-particle decay

The charge density wave system K 0.3 MoO 3 has been studied using variable pulse energy pump-probe spectroscopy, ellipsometry, and inelastic light scattering. The observed transient reflectivity response exhibits quite a complex behaviour, containing contributions due to quasi-particle excitations, coherent amplitudons and phonons, and heating effects. The generation of coherent amplitudons is discussed in terms of relaxation of photo-excited quasi-particles, and is found to be resonant with the interband plasmon frequency. Two additional coherent excitations observed in the transients are assigned to zonefolding modes of the charge density wave state.