Transmission and photoluminescence images of three-dimensional memory in vitreous silica

We demonstrate separate readouts of three-dimensional memory by (i) transmi ssion imaging using a conventional optical microscope and (ii) photolumines cence (PL) of the bits created by inducing optical damage within the vitreo us silica. Recording was done by tightly focused (objective x100, numerical aperture 1.3) single shot irradiation of 120 fs duration pulses at a 400 n m wavelength. For the readout, a broadband of PL at 470-600 nm was excited by 400 nm, 120 fs irradiation with pulse energy smaller by a factor of 10(6 ) compared with that for the recording. We found an erasing of the PL after 400 degrees C annealing, while the readability of the bits by the transmis sion was sustained. This shows the potential for two-bit information record ing per single bit by means of separate readout procedures. (C) 1999 Americ an Institute of Physics. [S0003-6951(99)05026-3].