Ultrafast near-infrared spectroscopic study of coherent phonons in the phase-separated manganite La1/4Pr3/8Ca3/8MnO3

We report the generation of coherent optical and acoustic phonons in mixed valent manganite La1/4Pr3/8Ca3/8MnO3 using femtosecond infrared pump-probe spectroscopy. Temperature-dependent measurements of the time-resolved optical reflectance, obtained over a range of 5-300 K, revealed that the energy of the photoexcited electrons dissipated during relaxation to acoustic phonons, in the high-temperature paramagnetic phase, and to optical phonons, in the low-temperature charge-ordering phase. Analysis of the temperature-dependent behavior reveals that the modal amplitudes of the coherent phonons appear strongly correlated with the charge-ordering phase.