• chalcogenide glasses;
  • optical switching;
  • pulsed-laser deposition;
  • X-ray photoelectron spectroscopy;
  • spectroscopic ellipsometry


Structural transitions in materials are accompanied by appreciable and exploitable changes in physical-chemical properties. Whereas reversible optically-driven atomistic changes in crystal-to-amorphous transitions are generally known and exploited in applications, the nature of the corresponding polyamorphic transitions between two structurally distinct meta-stable amorphous phases is an unexplored theme. Direct experimental evidence is reported for the nature of the atomistic changes during fully reversible amorphous-to-amorphous switching between two individual states in the non-crystalline As50Se50 films prepared by pulsed-laser deposition and consequent changes in optical properties. Combination of surface sensitive X-ray photoelectron spectroscopy and spectroscopic ellipsometry show that the near-bandgap energy illumination and annealing induce reversible switching in the material's structure by local bonding rearrangements. This is accompanied by switching in refractive index between two well-defined states. Exploiting the pluralism of distinct structural states in a disordered solid can provide new insights into the data storage in emerging optical memory and photonic applications.