1,720,968 research outputs found
Optical control of high-density alkali atom vapor in antirelaxation coated cells
Full text linkIn this work, we report on our investigations on LIAD (Light Induced Atomic Desorption) aimed at achieving high density of alkali atoms vapor in a coated cell at room temperature. The experimental results show the possibility to reach a density up to the limit when the medium becomes optically thick by applying highly efficient homogeneous illumination. The photon reabsorption mechanism prevents the precise evaluation of the density by measuring the absorption of a probe laser beam, but there is clear evidence that densities can be achieved higher by two orders of magnitude than the thermodynamic equilibrium value
Light-induced atomic desorption dynamics in cells with different coatings
No full textThe dynamics of Light-Induced Atomic Desorption (LIAD) in 6 cells with different coatings (PDMS coated cells prepared with two different concentrations of PDMS in ether, SC-77, PCHS, DCDMS, OTS) is investigated. The rates of desorption and adsorption of the Rb atoms when the illuminating light is switched ON and OFF and their dependence on the illuminating blue-light power are measured. The influence of the homogeneity of illumination for increasing the desorption and adsorption rates is evaluated. The results are interesting for the better understanding of LIAD and its dynamics and for the development of new optoelectronic elements, LIAD-loaded atomic devices and their miniaturization, and new methods for surface and coating diagnostics
Transformation of electromagnetically induced transparency into absorption in a thermal potassium optical cell with spin preserving coating
Full text linkWe 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
Light-induced atomic desorption in cells with different PDMS coatings
Full text linkLight-induced atomic desorption (LIAD) is a non-thermal process in which atoms adsorbed at a surface are released under illumination. It is applied mostly for realization of optical dispensers in the cases when high atomic density at low temperature is needed – for example, for loading atomic devices as atomic magnetometers, atomic clocks, magneto-optical traps and their miniaturization. However as desorption depends on the atom-surface interaction it can be applied for optical characterization and manipulation of alkali metal nanoparticles as well. In this work an experimental investigation of the shape of the transmission spectra and their dependence on the illuminating blue light power in PDMS coated cells prepared with two different concentrations of PDMS to ether is presented. Comparison with the LIAD effect in SC-77 coated and uncoated cells is done. All measurements are on the Rb D2 line in vacuum. The potential for application of these dependences for analysis of the quality of the coating surface and its optimisation is discussed
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Optical characterization of antirelaxation coatings
Full text linkAntirelaxation coatings (ARC) are used in optical cells containing alkali metal vapor to reduce the depolarization of alkali atoms after collisions with the cell walls. The long-lived ground state polarization is a basis for development of atomic clocks, magnetometers, quantum memory, slow light experiments, precision measurements of fundamental symmetries etc. In this work, a simple method for measuring the number of collisions of the alkali atoms with the cell walls without atomic spin randomization (Nasyrov et al., Proc. SPIE (2015)) was applied to characterize the AR properties of two PDMS coatings prepared from different solutions in ether (PDMS 2% and PDMS 5%). We observed influence of the light-induced atomic desorption (LIAD) on the AR properties of coatings
Antirelaxation coatings in coherent spectroscopy: Theoretical investigation and experimental test
No full textWe describe a theoretical model, based on a density matrix and the Liouville equation, for the investigation of magneto-optical resonances in alkali-metal atomic vapor, in particular in the case of the electromagnetically induced transparency (EIT) in the presence of antirelaxation coatings. The influence of the coating is parametrized with an empirical coefficient describing its efficiency; the calculations are extended to a broad range of coating quality, contrary to previous works, and to uncoated cells. The model takes into account also different configurations for the EIT formation and different efficiency of optical pumping, as determined by the coating characteristics and the atomic energy structure. The model is validated by investigating the EIT with degenerate Zeeman levels in K39 D1 and Cs D2 lines, which exhibit respectively an almost negligible and a relevant impact of hyperfine optical pumping. The results are compared to experimental data, exhibiting good agreement; in particular, for the K39 D1 line, recent findings are shown here in the case of degenerate and nondegenerate EIT with amplitude-modulated light. Our results demonstrate an effective approach for the investigation of antirelaxation coatings and their contribution in the formation of magneto-optical resonances in alkali-metal atoms, in different regimes and with largely different efficiencies. This sheds new light on well-known but not yet entirely clarified phenomena and their behavior as a function of experimental parameters
Optical characterization of antirelaxation coatings for photonics applications
No full textOptical characterization of antirelaxation coatings with regard to their applications in coherent spectroscopy and LIAD experiments is presented. A simple method, based on the recording of the fluorescence intensity of the Rb alkali atoms during resonant light pulse irradiation is used for comparison of the antirelaxation properties of the coatings. The LIAD yield and dynamics are measured by registration of the 780 nm Rb line transmission. The comparison of the parameters of PDMS coatings prepared with two different solutions in ether (PDMS 2% and PDMS 5%) shows that when illuminating with such LED intensity at which the LIAD efficiency is equal in the two cells, the light induced Rb vapor density changes are about an order of magnitude slower in the PDMS 2% cell, and the antirelaxation properties of the two cells are equal
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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