Multi-level coding-recoding by ultrafast phase transition on GeSbTe thin films.

Quickly switching among different states (levels) is crucial for reconfigurable metamaterials and devices. In this study, the dynamics of establishment and transformation of five amorphous or near-amorphous intermediate states with obvious optical contrasts on GeSbTe phase-change thin films driven by ultrashort laser pulses were investigated using real-time reflectivity measurements. The reversible coding-recoding among the five optical levels was realized by using single-shot picosecond laser pulses with designed fluences. The optical constants, crystalline states and surface morphologies before and after ultrafast multi-level coding were also compared and analyzed. These results may lay a foundation for the further design and application of dynamically reconfigurable optical/photonic devices.