70 research outputs found
Laser driven self-assembly of shape-controlled potassium nanoparticles in porous glass
We observe growth of shape-controlled potassium nanoparticles inside a random
network of glass nanopores, exposed to low-power laser radiation. Visible laser
light plays a dual role: it increases the desorption probability of potassium
atoms from the inner glass walls and induces the self-assembly of metastable
metallic nanoparticles along the nanopores. By probing the sample transparency
and the atomic light-induced desorption flux into the vapour phase, the
dynamics of both cluster formation/evaporation and atomic photo-desorption
processes are characterized. Results indicate that laser light not only
increases the number of nanoparticles embedded in the glass matrix but also
influences their structural properties. By properly choosing the laser
frequency and the illumination time, we demonstrate that it is possible to
tailor the nanoparticles'shape distribution. Furthermore, a deep connection
between the macroscopic behaviour of atomic desorption and light-assisted
cluster formation is observed. Our results suggest new perspectives for the
study of atom/surface interaction as well as an effective tool for the
light-controlled reversible growth of nanostructures.Comment: 14 pages,6 figures, http://iopscience.iop.org/1612-202X/11/8/085902
Transformation of electromagnetically induced transparency into absorption in a thermal potassium optical cell with spin preserving coating
We report a new experimental approach where an order of magnitude enhancement of the electromagnetically induced absorption (EIA) resonance contrast, thus making it similar to that of the EIT resonance contrast is observed under the same conditions. The EIA signal results from the interaction of a weak probe beam with a ground state that has been driven by the pump (counter-propagating) beam. Probe absorption spectra are presented where the laser frequency is slowly detuned over the D 1 line of 39 K vapor contained in a cell with a PDMS antirelaxation coating. In addition to the frequency detuning, a magnetic field orthogonal to the laser beams is scanned around zero value at a higher rate. With both laser beams linearly polarized, an EIT resonance is observed. However, changing the pump beam polarization from linear to circular reverses the resonance signal from EIT to EIA
Compact setup for the production of Rb-87 vertical bar F=2, m(F) =+2 > Bose-Einstein condensates in a hybrid trap
We present a compact experimental apparatus for Bose-Einstein condensation of 87Rb in the |F = 2, mF = + 2〉 state. A pre-cooled atomic beam of 87Rb is obtained by using an unbalanced magneto-optical trap, allowing controlled transfer of trapped atoms from the first vacuum chamber to the science chamber. Here, atoms are transferred to a hybrid trap, as produced by overlapping a magnetic quadrupole trap with a far-detuned optical trap with crossed beam configuration, where forced radiofrequency evaporation is realized. The final evaporation leading to Bose-Einstein condensation is then performed by exponentially lowering the optical trap depth. Control and stabilization systems of the optical trap beams are discussed in detail. The setup reliably produces a pure condensate in the |F = 2, mF = + 2〉 state in 50 s, which includes 33 s loading of the science magneto-optical trap and 17 s forced evaporation
Spin randomization of light-induced desorbed Rb atoms
We present the first experimental observation of atomic spin randomization of Rb atoms released by light-induced atomic desorption (LIAD). A natural mixture of Rb atoms contained in paraffin and PDMS coated glass cells is irradiated by a free-running diode laser light tuned to the Rb D2 resonance line. The transmission spectrum of the Rb vapor is thus modified and shows a strong enhancement of the hyperfine optical pumping as the light intensity is increased and the laser-frequency scanning rate is decreased. The D2 line spectra are compared for two cases: without and with illumination of the walls of the cell by a UV lamp centered around the wavelength of 404 nm. A simple theoretical model based on the solution of the rate balance equations is introduced in order to analyze the experimental results
Light-induced sodium desorption from paraffin film
Sodium photoejection from a paraffin coated cell has been
observed and analyzed in detail. The effect has been detected by observing the fluorescence induced by a cw dye laser. A maximum Na density of about 2.9 ×108 atoms/cm3 was obtained by shining the cell with 1.05 W Ar+ laser green light. A progressive slowing of the dynamics of the process is reported, probably due to a change in the chemical rearrangement of the Na atoms in the coating under intense light exposure. This aging effect represents a limitation in the practical application of this kind of materials
Analysis of High Efficiency Electromagnetically Induced Transparency in Potassium Vapor
We present a rate-equation theoretical model describing the optical pumping processes on the K line and we then discuss their influence on the electromagnetically induced transparency resonance parameters. We present also a comparison with the results of an experiment performed in cells containing pure alkali metal or added with a few torrs of buffer gas. The model shows that, in the last case, the complete Maxwellisation of the atomic population velocity distribution, along with the overlapping Doppler profiles of the transitions from the ground-states typical of K, leads to a partial compensation of optical pumping and a significant increase of the amplitude of the electromagnetically induced transparency resonances
Electromagnetic induction imaging with atomic magnetometers: Unlocking the low-conductivity regime
Electromagnetic induction imaging with atomic magnetometers has disclosed
unprecedented domains for imaging, from security screening to material
characterization. However, applications to low-conductivity specimens -- most
notably for biomedical imaging -- require sensitivity, stability, and
tunability only speculated thus far. Here, we demonstrate contactless and
non-invasive imaging down to 50 S/m using a 50 fT/Hz Rb
radio-frequency atomic magnetometer operating in an unshielded environment and
near room temperature. Two-dimensional images of test objects are obtained with
a near-resonant imaging approach, which reduces the phase noise by a factor
172, with projected sensitivity of 1 S/m. Our results, an improvement of more
than three orders of magnitude on previous imaging demonstrations, push
electromagnetic imaging with atomic magnetometers to regions of interest for
semiconductors, insulators, and biological tissues.Comment: 5 pages, 4 figures. Improved results. New manuscript layout.
Published version available, see https://doi.org/10.1063/1.511681
Analysis of High Efficiency Electromagnetically Induced Transparency in Potassium Vapor
We present a rate-equation theoretical model describing the optical pumping processes on the K line and we then discuss their influence on the electromagnetically induced transparency resonance parameters. We present also a comparison with the results of an experiment performed in cells containing pure alkali metal or added with a few torrs of buffer gas. The model shows that, in the last case, the complete Maxwellisation of the atomic population velocity distribution, along with the overlapping Doppler profiles of the transitions from the ground-states typical of K, leads to a partial compensation of optical pumping and a significant increase of the amplitude of the electromagnetically induced transparency resonances
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. (c) 2012 Optical Society of Americ
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