Up to now, the common media for optical data storage are the discs (blue ray technology forexample). However, by definition, this technology is limited to two dimensions. Thenecessity for increasing data storage capacity requires the use of three-dimensional (3D)optically based systems. One of the methods for 3D optical data storage is based on volumeholography. The physical mechanism is photochromism, which is defined as a reversibletransformation of a single chemical species between two states that have differentabsorption spectra and refractive indices. This allows for holographic multiplexingrecording and reading, such as wavelength (Rakuljic et al., 1992), angular (Mok, 1993), shift(Psaltis et al., 1995) and phase encoding. Another promising 3D optical data storage systemis the bit-by-bit memory at the nanoscale (Li et al., 2007). It is based on the confinement ofmulti-photon absorption to a very small volume because of its nonlinear dependence onexcitation intensity. This characteristic provides an income for activating chemical orphysical processes with high spatial resolution in three dimensions. As a result there is lesscross talk between neighbouring data layers. Another advantage of multi-photon excitationis the use of infrared (IR) illumination, which results in the reduction of scattering andpermits the recording of layers at a deep depth in a thick material. Two-photon 3D bitrecording in photopolymerizable (Strickler & Webb, 1991), photobleaching (Pan et al., 1997;Day & Gu, 1998) and void creation in transparent materials (Jiu et al., 2005; Squier & Muller,1999) has been demonstrated with a femtosecond laser. Recording densities could reachterabits per cubic centimeter. Nevertheless, these processes suffer from several drawbacks.The index modulation associated with high bit density limits the real data storage volumedue to light scattering. The fluorescence can limit the data transfer rate and the lifetime ofthe device.< Leer menos