Investigation of phase changes in Ge₁Sb₄Te ₇ films by single ultra-fast laser pulses

The phase transformations induced in a Ge₁Sb₄Te ₇ system by a femtosecond (fs) laser exposure were investigated. The system has a multilayer structure of 15 nm ZnS-SiO₂/80 nm Ge ₁Sb₄Te₇/100 nm ZnS-SiO₂/0.6 mm polycarbonate substrate. The morphology and contrast of marks formed in both amorphous and crystalline backgrounds by single fs pulses were characterized using an optical microscope. X-ray diffraction was applied to identify the crystal structures formed by single fs shots. Phase-reversible transformations in the system have been achieved through careful adjustment of the laser fluence. The mechanism of reversibility triggered by fs laser pulses is discussed. The feasibility of phase-change reversible optical recording with the active Ge₁Sb₄Te₇ layer using single fs pulses with a duration of 400 fs within well-defined fluence and pulse energy windows is therefore demonstrated. Our work also demonstrates that it is possible to record and retrieve data rapidly in the Ge₁Sb ₄Te₇ film within a conventional optical disk structure using non-amplified laser systems as laser sources.