Results 1 - 10 of 1195
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[en] This paper reports on conceptual and experimental work towards the realization of plasmonic surface traps for cold atoms. The trapping mechanism is based on the combination of a repulsive and an attractive potential generated by evanescent light waves that are plasmonically enhanced. The strength of enhancement can be locally manipulated via the thickness of a metal nanolayer deposited on top of a dielectric substrate. Thus, in principle the trapping geometry can be predefined by the metal layer design. We present simulations of a plasmonic lattice potential using a gold grating with sinusoidally modulated thickness. Experimentally, a first plasmonic test structure is presented and characterized. Furthermore, the surface potential landscape is detected by reflecting ultracold atom clouds from the test structure revealing the influence of both evanescent waves. A parameter range is identified where stable traps can be expected. (paper)
[en] Dye-doped hybrid silicate/titanium nanofilms on the glass substrate structures of asymmetrical waveguides were studied by way of laser systems. The threshold, spatial and spectral features of the laser oscillation of genuine and hollow waveguides were determined. The pattern of stimulated radiation included two concurrent processes: single-mode waveguide lasing and lateral small divergence emission. Comparison of the open angle of the lateral beams and grazing angles of the waveguide lasing mode provides an insight into the effect of leaky mode emission followed by Lummer–Gehrcke interference. (paper)
[en] The resonant-type contribution to the infrared absorption enhancement phenomenon was simulated using rigorous coupled wave analysis (RCWA) for well-defined periodic Au arrays. The Au arrays have size parameters compatible with those of vacuum-evaporated thin metal films, which are used conventionally for enhanced infrared absorption spectra measurements. Results obtained using RCWA technique show excellent quantitative agreement with both experimental observations of enhanced infrared absorption of adsorbed species and an electrostatic square column model calculation based on a non-resonant-type electromagnetic mechanism. This fact suggests that the resonant mechanism has a small contribution to the enhanced infrared absorption in an evaporated-film-like structure Au array. (paper)
[en] Temperature-dependent transmission experiments of ZnInSe thin films deposited by thermal evaporation method were performed in the spectral range of 550–950 nm and in temperature range of 10–300 K. Transmission spectra shifted towards higher wavelengths (lower energies) with increasing temperature. Transmission data were analyzed using Tauc relation and derivative spectroscopy. Analysis with Tauc relation was resulted in three different energy levels for the room temperature band gap values of material as 1.594, 1.735 and 1.830 eV. The spectrum of first wavelength derivative of transmittance exhibited two maxima positions at 1.632 and 1.814 eV and one minima around 1.741 eV. The determined energies from both methods were in good agreement with each other. The presence of three band gap energy levels were associated to valence band splitting due to crystal-field and spin–orbit splitting. Temperature dependence of the band gap energies were also analyzed using Varshni relation and gap energy value at absolute zero and the rate of change of gap energy with temperature were determined.
[en] Highlights: • A modified parallel electrode method (MPEM) was presented to make nanofibers. • MPEM could be used to optimize the performance of electrospun nanofibers. • Highly aligned nanofibers could be readily produced by the MPEM for a long time. • Theoretical analyses were carried out to study mechanical mechanism of MPEM. • The theoretical results were in good agreement with the experimental data. A modified parallel electrode method (MPEM) by placing a positively charged ring between the needle and the parallel electrode collector was presented to fabricate highly aligned electrospun nanofibers. The experimental and theoretical analyses were carried out to study mechanical mechanism of the MPEM. As a result the ring could be used to optimize and control the nanofiber alignment, and an optimal ring voltage was determined. In addition, the effectiveness of the MPEM was demonstrated by measuring the diameter distribution and the degree of nanofiber alignment. And the results showed the MPEM could decrease the nanofiber diameter, enhance the diameter distribution, and improve the nanofiber alignment two times more than the parallel electrode method (PEM).
[en] We analyze the error associated with the optical transition matrix element spectral dependencies for hydrogenated amorphous silicon and crystalline silicon found by Jackson et al. (Phys Rev B 31:5187–5198, 1985). We find that this error is considerable for photon energies less than 1.5 eV. This suggests that spectral dependencies for the optical transition matrix element, other than those proposed by Jackson et al., are possible for photon energies less than 1.5 eV. With this limitation in mind, we then fit a Lorentzian peak to the crystalline silicon experimental optical transition matrix element result of Jackson et al. Within the framework of the damped harmonic oscillator perspective, plotting the term related to the location of the resonant frequency as a function of the damping coefficient, for a number of thin-film silicon experimental results, we have found a relationship between these model parameters. We suspect that this dependence has important implications for the optical response of various forms of thin-film silicon and related materials.
[en] The present study analytically investigates the Love-type wave vibrations in a piezoelectric thin film with highly and weakly dielectric conducting interface with pre-stressed elastic plate. Dispersion equations are obtained analytically for both electrically open and short cases together with highly and weekly interfaces in the transcendental complex form. Outcomes specify that microstructures consisting flexoelectricity has an essential influence on dispersion features of the Love-type wave and also affected by the conducting interface. As a remarkable outcome, complex phase velocity with positive imaginary part increases with time. Moreover, the dispersion relation depends substantially on the flexoelectric coefficients and width of the guiding plate. The present study is the prior attempt to show the flexoelectricity influence with weekly and highly conducting interfaces. (paper)
[en] We study the force of light on a two-level atom near an ultrathin optical fiber using the mode function method and the Green tensor technique. We show that the total force consists of the driving-field force, the spontaneous-emission recoil force, and the fiber-induced van der Waals potential force. Due to the existence of a nonzero axial component of the field in a guided mode, the Rabi frequency and, hence, the magnitude of the force of the guided driving field may depend on the propagation direction. When the atomic dipole rotates in the meridional plane, the spontaneous-emission recoil force may arise as a result of the asymmetric spontaneous emission with respect to opposite propagation directions. The van der Waals potential for the atom in the ground state is off-resonant and opposite to the off-resonant part of the van der Waals potential for the atom in the excited state. Unlike the potential for the ground state, the potential for the excited state may oscillate depending on the distance from the atom to the fiber surface. (paper)