Ultrafast laser-induced phase transitions in amorphous GeSb firms

Time-resolved measurements of the spectral dielectric function reveal new i nformation about ultrafast phase transitions induced by femtosecond laser p ulses in Sb-rich amorphous GeSb films. The excitation generates a nontherma l phase within 200 fs. The dielectric function of this phase differs from t hat of the crystalline phase, contrary to previous suggestions of a disorde r-to-order transition. The observed dielectric function is close to that of the liquid phase, indicating an ultrafast transition from the amorphous ph ase to a different disordered state.