Photo-induced phenomena in NaV2O5 studied by time-resolved Raman spectroscopy

Time-resolved Raman measurements were performed in a spin ladder system α′-NaV2O5 in picoseconds time range. We observed the rapid decrease and gradual recovery of the peak intensity at 66 cm−1 due to the superlattice structure in the low-temperature phase by photoexcitation. The decay and recovery time constants from a fitting by the double exponential function are 5 and 800 ps, respectively. The transient changes of the local temperature of the sample surface were determined from the intensity ratio of the anti-Stokes and Stokes scattering. The result shows that the highest temperature of 23 K at 20 ps is far below the phase transition temperature of 34 K and the phase change does not occur by laser heating. The temporal changes of the Raman intensities are ascribed to the decrease of the order parameter in the superlattice structure induced by optical pumping in the low-temperature phase.