Rewritable multilevel optical storage based on valence state conversion induced by phase-shaped femtosecond laser in rare earth-doped nanocrystals

Optical storage based on femtosecond laser-induced valence state conversion (VC) in solid materials has garnered significant interest due to its excellent readability and high signal-to-noise ratio. Previous VC-based optical storage studies adopting femtosecond lasers are typically binary, which significantly limits data capacity. Here, we develop a VC-based multilevel optical storage method utilizing a phase-shaped femtosecond laser. Multiple digital numbers are encoded into the VC efficiencies by modulating the laser spectral phase and decoded from the relative luminescence intensities of photoinduced ions. A proof-of-principle experiment of six-digit optical storage is conducted, demonstrating good feasibility of the method. In addition, by encoding different colors into the various VC efficiencies, an artificial six-color flower pattern is stored. The colorful flower pattern can be readily erased and recorded again, showing good rewritability of the sample. Our method provides a convenient and promising solution for high-capacity data storage and encryption.