Dark matter (DM) represents one of the most intriguing challenges of modern physics, both for the theoretical predictions and for the experimental setups. The search for the possible DM component candidates regards a wide range of objects and of energy values. In order to detect processes related to very weak interactions, as expected in these cases, it is necessary to improve the performances of the available detectors making them more efficient in terms of energy threshold and mass. Here we present a research activity aimed at the development of a novel type of detector based on laser interrogation of atomic energy levels for species that have been loaded in a solid matrix of a non interacting material at very low temperatures. The laser assisted transitions are only promoted when an incident particle is absorbed in the material, releasing its energy to the embedded atoms. The detection can be obtained via both optical and electronic methods.
COSMA: Coherent Optics Sensors for Medical Application is an European Marie Curie Project running from 2012 to March 2016, with the participation of 10 teams from Armenia, Bulgaria, India, Israel, Italy, Poland, Russia, UK, USA. The main objective was to focus theoretical and experimental research on biomagnetism phenomena, with the specific aim to develop all-optical sensors dedicated to their detection and suitable for applications in clinical diagnostics. The paper presents some of the most recent results obtained during the exchange visits of the involved scientists, after an introduction about the phenomenon which is the pillar of this kind of research and of many other new fields in laser spectroscopy, atomic physics, and quantum optics: the dark resonance.
In this work we present new features observed in the Saturated Absorption (SA) spectrum on the D<sub>1</sub> line of K. In an
uncoated optical glass cell containing pure K atoms, excitation by circularly polarized pump beam produces an
enhancement of the amplitude of the crossover resonances due to the hyperfine transitions starting from the ground state
F<sub>g</sub> = 2. This effect appears to be much more relevant when K atoms are contained in a cell coated with an anti-relaxation
film. Here, the crossover resonance in the F<sub>g</sub> = 2 set of transition is not observed experimentally with linearly polarized
pump light, while in case of circular polarization its amplitude is significantly enlarged. The Light Induced Atomic
Desorption (LIAD) effect strongly improves the intensities of the SA resonances observed in coated cell.
This paper presents the recent results of the TrapRad/Francium collaboration whose final aim is the measurement of the Atomic Parity Non-Conservation effect (APNC) in Francium atoms stored in a Magneto – Optical Trap (MOT) built at the Laboratori Nazionali di Legnaro (LNL) of the National Institute for Nuclear Physics (INFN). Current developments and new strategies to enhance the trapping efficiency of Francium isotopes and to detect new spectroscopic features are reported.
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.
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.
Magnetic coherence resonance profiles, obtained at magetic field B = O in Hanle configuration were examined for Na and K atoms in different cells: evacuated glass cells and buffered, coated and uncoated. At low laser power for all cells the shape of the resonancees is Lorentzian. At power higher than about 100 mW/cm<sup>2</sup>, some narrowing around the resonance peak is observed for the Na buffered cell, while for the vacuum one the resonance shape is even more complex. Theoretical explanation is proposed for the complex resonance shape evidenced in the vacuum cells. Large resonance contrast in the K absorption at B = 0 is observed, attributed to the low rate of hyperfine optical pumping in K. The detailed investigation of the resonance profiles and contrast is of very high importance for their application.
A simple set-up for observation of CPT effect at single hyperfine ground state excitation has been examined for application in measurements of non-vanishing magnetic fields. The CPT is prepared using low-frequency modulated (in the kHz range) diode laser. Magnetic field measurements down to 500 pT sensitivity and reproducibility were obtained for integration time of 30 ms. One of the important characteristics of the proposed methodology is a proper Cs excitation in order to overcome effectively the huperfine optical pumping effefct. This is possible working in narrow ranges of laser beam intensity, buffer gas pressures and Cs vapor densities. The best conditions have been experimentally determined and discussed.
Investigation on coherent population trapping and electromagnetic induced absorption effects has been made in Cs vapors. A detailed analysis of degenerate and non-degenerate cases is reported. Possible application to precise magnetic field measurements is discussed and preliminary results described.
In this paper we propose a simple method for eliminating the population losses of MC resonances by involving all atoms of the Na ground state in the formation of the narrow coherent resonances observed in the fluorescence when scanning around zero value the applied magnetic field. As a result, dark resonances with a contrast up to 100% have been observed. Results are obtained in two different experimental configurations: using laser excitation of linear and circular polarization, leading to different population redistribution among Zeeman and hf levels. Theoretical analysis of the results is also presented. It is shown that at certain conditions complete optical pumping of atoms to levels F<sub>g</sub>=2, m<sub>Fg</sub>=2 or m<sub>Fg</sub>=-2 can be achieved, which means complete orientation of the atoms.
Laser cooling and trapping techniques made possible during the last two decades important achievements in the atomic physics and quantum mechanics fields. These same techniques can be usefully applied to radioactive atoms by opening new fields of investigations. Nuclear processes can be studied with the atomic physics tools. We focused our attention on Francium radioactive atoms. A magneto-optical trap has been set up at the INFN Legnaro laboratories. Preliminary tests with other stable alkali atoms aimed at an improvement of the MOT collection efficiency are reported. Fast and efficient trap loading of rubidium has been obtained through the light-induced atomic desorption from an organic coating. A larger number of sodium atoms, as compared to monochromatic trapping laser, has been trapped by using a broad-band laser.
Temperature dependences of coherent resonances in Na and Cs atoms prepared by two coherent laser frequencies or two polarizations of single frequency laser field are presented. It is shown that the temperature dependence of the amplitude or contrast of the resonances in most cases exhibits a maximum. For both types of coherent resonances, a reason for the contrast reduction at higher temperature is the increased absorption of the laser light along the gas cell due to the optical thickness of the medium. Spin-exchange collisions lead to resonance contrast reduction more effectively in a cell with pure alkali atoms.
Light induced atomic desorption (LIAD) is an impressive manifestation of a new class of phenomena involving alkali atoms, dielectric films and light. LIAD consists of a huge emission of alkali atoms (experimentally proved for sodium, potassium, rubidium and cesium) from siloxane films when illuminated by laser or ordinary light. Most of the experiments have been performed in glass cells suitably coated by a thin film (of the order of 10 micrometer) either of poly - (dimethylsiloxane) (PDMS), a polymer, or of octamethylcyclotetrasiloxane (OCT), a crown molecule. LIAD is a combination of two processes: direct photo-desorption from the surface and diffusion within the siloxane layer. The photo-desorbed atoms are replaced by fresh atoms diffusing to the surface. Moreover, from the experimental data it comes out that the desorbing light increases atomic diffusion and hence the diffusion coefficient. To our knowledge this is the first time that such an effect is clearly observed, measured and discussed: LIAD represents a new class of photo-effects characterized by two simultaneous phenomena due to the light: surface desorption and fastened bulk diffusion.
The resonant radiation pressure effect induced by `white' laser radiation is discussed. Experimental results on atomic beam deceleration and vapor compression induced by the resonance radiation pressure effect are reported. The `white' laser radiation has been simulated by a multimode long cavity dye laser.