Thermal and non-thermal photoinduced phenomena in α'-NaV₂O₅

Transient reflectance changes induced by pulsed photo-excitation with 1.55 and 3.1 eV photons were studied in sodium vanadate, α'-NaV₂O₅. At low excitation densities, the response shows a slow rising with a time constant of 3 ps, while at higher excitation density, the rising becomes fast with a time constant of 500 fs. Oscillation in reflectance was also observed and ascribed to an acoustic phonon burst. The transient spectra were compared to the temperature difference reflectance spectra, and the photocreated states are understood as the high-temperature state of the high-temperature phase. On the other hand, the fast-rising components are ascribed to non-thermal creation of the charge-disordered phase.