Andrea Bogi

Full control of sodium vapor density in siloxane-coated cells using blue LED light-induced atomic desorption

We propose and experimentally implement a method, based on light-induced atomic desorption, for controlled generation of large sodium densities in siloxane-coated cells, kept at room temperature. An array of blue LEDs is used to desorb sodium atoms from the cell walls. The required atomic vapor density is achieved and stabilized by controlling the LED power through the feedback given by the sodium fluorescence. We show that sodium densities corresponding to about 400 K can be obtained and kept stable for a long time with less than 6 mW of LED light power. Moreover, this technique allows for precise vapor density modulation with a frequency of tenths of hertz, which is not possible using traditional heating methods.

Optical recording in Rb loaded-porous glass by reversible photoinduced phase transformations

We report reversible phase transformations in Rb loaded-porous glass irradiated with weak laser light which allow us to realize image storage on it. The effect is due to photo-induced changes of Rb distribution inside the glass pores, where atomic photodetachment and confinement produce either formation or evaporation of Rb nanoclusters. These processes depend on light frequency and intensity making controllable by light the porous glass transparency. We demonstrate that porous glass doped with Rb can be used as a support to record a light pulse for a long time as well as to remember the order of light colors in an illumination sequence.

Light-induced atomic desorption and related phenomena

We review some recent studies on light-induced atomic desorption (LIAD) from dielectric surfaces. Alkali-metal atoms adsorbed either on organic films or on porous glass are released into the vapor phase under illumination. The measurements were performed in Pyrex resonance cells either coated with siloxane films or containing a porous glass sample. In both cases, the experimental results show that LIAD can be used to produce atomic densities suitable for most atomic physics experiments. Moreover, we find that photoinduced effects, correlated with LIAD, produce reversible formation and evaporation of alkali-metal clusters in porous glass. These processes depend on the light frequency, making the porous glass transmittance controllable by light.

All-optical vapor density control for electromagnetically induced transparency

We demonstrate the feasibility of coherent spectroscopy experiments in alkali vapors at room temperature by using an automatic all-optical atomic dispenser. The reliability of the system is proved by observing electromagnetically induced transparency (EIT) resonances in siloxane-coated cells where large and stable K densities are achieved by light-controlled atomic desorption from the cell coating. The experimental results prove that this technique preserves the orientation of the atomic system, and, at the same time, allows a fine, continuous, and rapid control of the vapor density also suitable for magnetic-sensitive applications.

Optical stabilization of Rb vapor density above thermal equilibrium

We stabilize the Rb vapor density above its thermal equilibrium value in sealed glass cells, which are generally used in atomic physics experiments. The method relies on light-induced desorption of Rb atoms from dielectric surfaces. The process does not demand high light intensities so that LEDs or laser diodes can be used as desorbing sources. The experiments are carried out in Pyrex cells either coated with a polydimethylsiloxane film or containing a porous glass sample. Under illumination both the organic coating and the porous sample release a large amount of Rb atoms into the cell volume. We show that the Rb vapor density can be maintained to a preset value, using a desorbing light intensity controlled by a feedback signal given by the Rb absorption or fluorescence level. Moreover, we find that the stabilization technique does not depend on the microscopic mechanisms underlying photodesorption.

Light-induced atomic desorption from siloxane film loaded with Rb and Cs

We observe Light-induced atomic desorption (LIAD) of Rb and Cs atoms from a PDMS-coated cell containing both atoms at the same time. The desorption rate and the relative vapor density variation have been simultaneously measured for both alkali atoms as a function of the desorbing light intensity and frequency. They show the same behaviour upon the different illumination conditions. This work demonstrates the possibility to provide light controlled atomic dispenser delivering different atomic species using the LIAD effect.

Atomic sources controlled by light: Main features and applications

We present in this paper recent results on Light - Induced Atom Desorption (LIAD) in sealed and open coated cells. LIAD is defined via the description of an experiment on rubidium atoms stored in a dry - film coated cell, where a few milliwatts of even non coherent and non resonant light are able to increase the alkali atomic density for more than one order of magnitude. Modeling of the effect is given. New features become relevant in the case of LIAD in porous glasses: in fact, although the photodesorption efficiency per unit area in bare glass is much lower, photoatomic sources can be prepared, due to the huge inner surface of porous samples. We applied LIAD from organic coatings to the stabilization of alkali densities out of equilibrium: sodium case is here discussed. Finally, we report on fully original, preliminary measurements of rubidium Magneto - Optical Trap loading via LIAD from a dry - film coated cell.

Light-induced atomic desorption from PDMS films and porous glass: application and fundamental issues

Light-induced desorption and diffusion of alkali atoms embedded in dielectric substrates are experimentally and theoretically investigated. The goal is to realize atomic dispensers fully controlled by light, to study the atom-dielectric interaction and to make spectroscopy of atoms confined in micro-nano structures. Very interesting results have been obtained with Rb and Cs in PDMS films and porous glasses.

Light-induced processes on atoms and clusters confined in nanoporous silica and organic films

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.

Photo-ejection and transport of alkali atoms embedded in nano-porous silica

Recently we observed non-thermal photoejection of atoms embedded in nano-porous silica samples. Alkali atoms are stored inside porous glass matrices and then they are desorbed by ordinary or laser light. In this paper, we present an experimental investigation of the dependence of photodesorption dynamics on desorbing radiation, showing that light induced effects on alkali nano-particles, dispersed in the glass matrix, are started up upon specific conditions of the incident radiation. On the basis of this study, we find that the light is able both to drive the atomic flux from the glass surface and to modify the optical properties of the glass samples, opening interesting perspectives for applications.