The study of light induced processes on atoms and nanoparticles confined in organic films or in dielectric structures is
motivated both by fundamental interest and applications in optics and photonics. Depending on the light intensity and
frequency and the kind of confinement, different processes can be activated. Among them photodesorption processes
have a key role. Non thermal light induced atomic desorption has been observed from siloxane and paraffin films
previously exposed to alkali vapors. This effect has been extensively investigated and used both to develop photo-atom
sources and to load magneto-optical traps. Recently we observed huge photodesorption of alkali atoms embedded in
nanoporous silica. In this case the atomic photodesorption causes, by properly tuning the light frequency, either
formation or evaporation of clusters inside the silica matrix. Green-blue light desorbs isolated adatoms from the glass
surface eventually producing clusters, whereas red-near infrared (NIR) light causes cluster evaporation due to direct
excitation of surface plasmon oscillations. Green-blue light induces cluster formation taking advantage of the dense
atomic vapor, which diffuses through the glass nano-cavities. Both processes are reversible and even visible to the naked
eye. By alternatively illuminating the porous glass sample with blue-green and red-NIR light we demonstrate that the
glass remembers the illumination sequences behaving as an effective rereadable and rewritable optical medium.
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