Ultrafast optical phase response associated with photoinduced phase transition in VO2

VO₂ is a prototypical strongly correlated material known to undergo photoinduced phase transitions on the femtosecond scale. To explore its potential for ultrafast all-optical phase modulation, we constructed a femtosecond time-resolved interferometer to directly probe the optical phase response, revealing the change in the real part of the refractive index during the phase transition. The observed optical phase dynamics exhibit faster and slower components, reflecting different stages of the phase transition process. The overall magnitude of the phase shift is largely determined by the ultrafast response, demonstrating the feasibility of femtosecond all-optical phase modulation in VO₂ thin films.