Reversible Structural Modulation of Ge ₂ Sb ₂ Te ₅ -Modified Nanogratings via Femtosecond Laser Imprinting for Dynamic Photonic Applications

Reconfigurable optical devices require nanoscale control over both the material properties and the structural morphology. This study demonstrates a femtosecond laser-based imprinting technique that achieves reversible structural modulation in Ge2Sb2Te5 (GST) phase-change nanostructures by leveraging its significant density variation during phase transition, rather than conventional dielectric tuning. We show precise control over the grating geometry, enabling polarization-selective optical responses for multiplexed information recording and reading. Applications including dual-pattern storage, multidimensional encryption, and dynamic structural color displays are realized, highlighting the versatility of this approach. Ultrafast pump–probe spectroscopy and high-resolution transmission electron microscopy reveal the microstructural dynamics during cyclic phase transitions, identifying a transition from homogeneous to heterogeneous nucleation accompanied by crystal reorientation from [001] to [011]. The erasure process is complete within 50 ps, while grain refinement, lattice reorganization, and defect accumulation collectively contribute to gradual degradation in cyclic endurance. This work establishes a generalizable framework for reversible structural modulation in functional materials with potential applications in reconfigurable photonics, secure communications, and adaptive optics.