Femtosecond-Laser Writing of Microbits for Luminescent Memory in Sapphire

The modification of the bulk of synthetic optical-grade sapphire by focused (NA = 0.55) 150-fs laser pulses with a wavelength of 525 nm results in the formation of 2 × 2 × 25-µm 3 regions where luminescence in the 700–850 nm band, associated with the formation of multicomponent complexes involving F 2 and F₂^2 + vacancies and Cr 3+ ions, is enhanced. For pulse energies of 5–22.5 nJ, the sapphire crystal lattice remains undamaged, which makes this process promising for writing three-dimensional microcodes for luminescent memory with capacities as high as 10 Gbit/cm 3 suitable for error-free readout under single-photon laser excitation.