Single femtosecond laser pulse–induced valence state conversion in BaFCl: Sm³⁺ nanocrystals for low-threshold optical storage

Femtosecond laser-induced valence state conversion (VC) in solid materials has attracted significant research attention due to its potential application in ultra-high density optical storage, boasting advantages such as ultra-high recording speed, easy reading, and high signal-to-noise ratio. However, identifying appropriate materials and technological solutions conducive to efficient single-laser-shot recording remains a pivotal challenge for practical applications. In this work, we report single femtosecond laser pulse–induced VC in BaFCl: Sm³⁺ nanocrystals utilizing a 4F-configuration optical imaging system comprising two-dimensional scan galvo mirrors. For the first time, we experimentally reveal the luminescence mechanisms and channels of multiphoton absorption-induced Sm²⁺ ions under both single and multiple 800 nm fs laser pulses. Leveraging the highly efficient single femtosecond laser pulse induced VC, we demonstrate a prototype optical storage experiment by sweeping the recording laser pulse. Remarkably, a threshold pulse energy as low as ∼100 nJ for effective single-laser-shot recording in BaFCl: Sm³⁺ nanocrystals is obtained under the current experimental conditions. Our investigations offer profound insights into the physical mechanisms underlying femtosecond laser induced VC in solid materials, thereby promoting the prospects of VC based optical storage toward practical applications.