Time-resolved measurements of the spectral dielectric function reveal new information about ultrafast phase transitions induced by femtosecond laser pulses in Sb-rich amorphous GeSb films. The excitation generates a nonthermal phase within 200 fs. The dielectric function of this phase differs from that of the crystalline phase, contrary to previous suggestions of a disorder-to-order transition. The observed dielectric function is close to that of the liquid phase, indicating an ultrafast transition from the amorphous phase to a different disordered state.

• Received 15 September 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.3650