The Legnaro Francium Magneto-Optical Trap

Hyperfine Interactions - Laser cooling and trapping of radioactive atoms represent the new frontier in atomic physics and a new powerful tool in nuclear physics. We are setting up at the...     

Optical characterization and manipulation of alkali metal nanoparticles in porous silica

Rubidium and cesium metal nanoparticles were grown in nanoporous silica samples placed in alkali vapor cells. Their size and shape were investigated by measuring the sample optical transmittance. Spectral changes due to photodesorption processes activated by weak light were also analyzed. Alkali atoms photoejected from the silica walls diffuse through and out of the nanopores, modifying both the nanoparticle distribution in the silica matrix and the atomic vapor pressure in the cell volume. The number of rubidium and cesium atoms burst out of the samples was measured as a function of photon energy and fluence. The optical absorption measurements together with the analysis of the photodesorption yield give a complete picture of the processes triggered by light inside the nanopores. We show that atomic photodesorption, upon proper choice of light frequency and intensity, induces either growth or evaporation of nanosized alkali metal clusters. Cluster size and shape are determined by the host-guest interaction.     

Desorption of Rb and Cs from PDMS induced by non resonant light scattering

Simultaneous light-induced desorption of rubidium and cesium atoms has been observed in polydimethylsiloxane (PDMS) coated Pyrex cells at room temperature and at low light intensity. The two alkali atoms show the same dynamics and the same dependence on the desorbing light frequency. No competition in the free sites occupancy exists. An interpretation of the experimental results in terms of non-resonant light scattering from the PDMS coating is discussed.     

Dynamics of laser-induced cesium atom desorption from porous glass

The dynamics of short pulsed infrared laser-induced desorption of Cesium atoms from porous silica samples has been investigated. We find most probable kinetic energies of 69 ± 6 meV for desorption laser fluences between 60 and 190 mJ/cm², significantly higher compared to those obtained for Cs desorption from plain glass, 40 ± 2 meV, but lower compared to those observed for Na and Rb desorption from polymeric surfaces, 200 meV. This is explained qualitatively by scattering of the desorbing atoms with the silica nanochannels, thus suggesting different pulsed laser photodesorption processes for atoms embedded in hard porous dielectrics as compared to polymeric thin films.     

Reversible light-controlled formation and evaporation of rubidium clusters in nanoporous silica

We observe reversible light assisted formation and evaporation of rubidium clusters embedded in nanoporous silica. Metallic nanoparticles are cyclically produced and evaporated by weak blue-green and near-infrared light, respectively. The atoms photodetached from the huge surface of the silica matrix build up clusters, whereas cluster evaporation is increased by induced surface plasmon excitation. Frequency tuning of light activates either one process or the other and the related changes of glass transparency become visible to the naked eye. We demonstrate that the porous silica, loaded with rubidium, shows memory of illumination sequences behaving as a rereadable and rewritable optical medium. These processes take place as a consequence of the strong confinement of atoms and particles at the nanoscale.     

Light induced atomic desorption from dry-film coatings

We report the first experimental evidence of nonthermal light induced atomic desorption (LIAD) from octadecyltrichlorosilane dry film. The experiment has been made with Rb confined in a coated cell kept at room temperature. A detailed study of the main features of LIAD effect has been made by varying intensity and wavelength of desorbing light. A discussion about the differences and similarities with other organic films that were studied first is reported. This result is important as it expands the list of materials showing such an effect and increases the possibilities to get suitable light controlled atomic sources for spectroscopy and applications. In particular, we plan to exploit this feature in a Fr magneto-optical trap apparatus.     

A new class of photo-induced phenomena in siloxane films

The light induced atomic desorption effect, known as LIAD, is observed whenever Pyrex cells, coated with siloxane films and containing alkali atoms, are illuminated. LIAD is a non-thermal phenomenon and it can be observed even with very weak light intensities. We show that the simultaneous contribution to the photo-emission of atoms adsorbed both at the film surface and within the film must be taken into account in order to fit the experimental data. We demonstrate that both the desorption efficiency and the diffusion coefficient of the alkali atoms embedded in the dielectric film depend on the desorbing light intensity. These features characterize a new class of photo-induced phenomena whose analysis gives new insights in the comprehension of the atom-surface interaction and of the atom-bulk diffusion and opens interesting perspectives for applications. Received 27 April 2000 and Received in final form 15 September 2000