Results 1 - 10 of 1226
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[en] In this paper we provide a detailed analysis of heat generation in a solid-state laser medium. The fractional thermal loadings are different for different physical processes in a laser medium, including the fluorescence process, stimulated emission, energy transfer up-conversion and excited-state absorption. Applying this theoretical analysis in a diode-end-pumped Nd:GdVO4 laser at 1342 nm, and using a simple and efficient method to measure the thermal loading of the solid-state laser medium presented, the experimental results are in good agreement with the theoretically calculated results. (paper)
[en] The molecular R-matrix formalism is used to calculate bound and continuum states of the CH molecule. Potential energy curves for the bound states of doublet and quartet symmetry are obtained for an extended range of inter nuclear distances between 1–9 a.u. Resonance positions and widths for low-lying Feshbach resonances are also obtained for states with doublet symmetry. These resonances and their continuation as bound states below the CH+ ion ground state are used to construct dissociative states which cross the ground state of the CH+ ion. Several dissociative states of , and symmetry, that were hitherto unknown, have been found and are expected to be useful for other collisional calculations, in particular, for the dissociative recombination of the CH+ ion. (paper)
[en] Nonlinear mechanisms are frequently invoked to explain unexpected observations during processes of energy exchange in mechanical systems. However, whether the same phenomena could be observed in a purely linear system is seldom considered. In this paper, we revisit the problem of two linearly coupled, damped, harmonic oscillators, with emphasis on the dynamics of their mutual exchange of energy. A novel criterion is established to discern between two well-differentiated regimes of energy exchange under ringdown conditions, when all external excitations are turned off and the oscillatory motion is left to decay by dissipation. The two regimes are induced by different sets of initial conditions, and correspond to extremal values of the total net energy transferred during ringdown. Although the problem is in principle fully solvable, its algebraic involvedness requires in practice to resort to approximated expressions for oscillation frequencies and decay rates. We explicitly provide such approximations in the limit of high quality factors and weak coupling. This limit is relevant to current experiments on micro- and nanomechanical oscillators, whose physical behavior is usually explained by extensive allusion to energy exchange. Our results should help to discern between observations that are genuinely due to nonlinear effects, and those that can be explained in terms of linear mechanisms only. (paper)
[en] The work is devoted to the investigation of the weakly bound three-body atomic clusters. The calculations on the van der Waals trimer 7Li4He2 are carried out using the differential Faddeev equations, which allows us to give accurate binding energies for both the ground and the exited state of the system. The results obtained indicate the Efimov nature of the excited state in this system.
[en] High power tapered lasers are designed and fabricated. A one-dimensional photonic crystal structure in the vertical direction is adopted to narrow the far field divergence. The thickness of the defect layer and the photonic crystal layers are optimized by analyzing the optical field theoretically. For tapered lasers, the continuous-wave power is 7.3 W and the pulsed power is 17 W. A maximum wall-plug efficiency of 46% under continuous-wave operation and 49.3% in pulsed mode are obtained. The beam divergences are around 11° and 6° for the vertical and lateral directions, respectively. High beam qualities are also obtained with a vertical M2 value of 1.78 and a lateral M2 value of 1.62. As the current increases, the lateral M2 value increases gradually while the vertical M2 value remains around 2. (paper)
[en] Ultracold atom experiments allow the study of topological insulators, such as the non-interacting Haldane model. In this work we study a generalization of the Haldane model with spin–spin on-site interactions that can be implemented on such experiments. We focus on measuring the winding number, a topological invariant, of the ground state, which we compute using a mean-field calculation that effectively captures long-range correlations and a matrix product state computation in a lattice with 64 sites. Our main result is that we show how the topological phases present in the non-interacting model survive until the interactions are comparable to the kinetic energy. We also demonstrate the accuracy of our mean-field approach in efficiently capturing long-range correlations. Based on state-of-the-art ultracold atom experiments, we propose an implementation of our model that can give information about the topological phases. (paper)
[en] The adiabatic potential energy curves, permanent and transition dipole moments (TDMs) of the highly-excited states of the MgK+ molecular ion have been computed as a function of the inter-nuclear distance R. The results are obtained by an ab initio approach involving a non-empirical pseudo-potential for the Mg and K cores, correlation treatment for core valence through an effective core polarisation potential, and full valence configuration interaction. The molecule is thus treated as a two electron system. Ab initio electronic TDM functions are calculated for all dipole-allowed transitions among the 42 states of MgK+. Many of these moment functions exhibit interesting behaviour due to charge transfer or ion-atom pair correlations. The positions of a number of satellite bands are predicted from the potential energy difference curves. We verified our results by performing complete active space self-consistent field calculations followed by a multireference configuration interaction and including Davidson correction. We observe a rather good agreement for most of them especially for the ground and lower excited states. We investigate ion-atom cold collisions at quantum regime. Furthermore, we explore ion-atom elastic collisions at low temperatures, predicting the formation of translationally and rotationally cold molecular ion MgK+ in the ground state electronic potential by stimulated Raman type process. Our results are important in the perspective of upcoming experiments aiming at merging cold alkali atom and alkaline-earth ion in a hybrid trap for the creation of cold molecular ions by photoassociation. (paper)
[en] The dependence of the cross section for the C + SH H + CS, S + CH reactions on the vibrational excitation of SH(v = 0–20, j = 0) is analyzed in detail at the collision energies of 0.3 and 0.8 eV by using the quasi-classical trajectory method and the new potential energy surface (Song et al 2016 Sci. Rep. 6 37734) of the . The efficiency of vibrational excitation to promote the reaction is investigated through the analysis of the cross section and its v dependence in terms of the reaction probability, maximum impact parameter, and the features of the potential energy surface. The differential cross sections obtained show that at higher vibrational levels, the products (CS, CH) are mainly forward scattered, and the sideward and backward scatterings are quite weak. In addition to the scalar properties, the stereodynamical attributes, such as angle distribution functions P(θ r), P(ϕ r) and P(θ r, ϕ r) at different vibrational levels are explored in detail. Furthermore, through the investigation of the state-to-state dynamics for the titled reaction, it is clear that the vibrational excitation of the product for C + SH H + CS reaction is quite strong, with the most probable population appearing at high vibration numbers. (paper)
[en] Photothermal conversion is one of the most effective ways of absorbing and utilizing solar energy. The key issues of photothermal conversion are seeking for nanofluids with strong and wide-range sunlight harvesting. In this work, near-infrared (NIR) light absorbed Bi2WO6 is first exploited for solar thermal conversion. However, the photothermal conversion efficiency is low owing to its insufficient NIR-light absorption. After coating Au nanoparticles on Bi2WO6 nanosheets, the localized surface plasmon resonance effect of Au nanoparticles enable Bi2WO6 show strong optical absorption. Au/Bi2WO6–H2O nanofluids have higher temperature rise and better photothermal conversion efficiency than Bi2WO6 and the base fluid water. The present work not only explore a new way for improving the photothermal conversion efficiency of NIR-light nanofluids, but also help design and prepare novel broad-band sunlight absorption nanofluids.
[en] LiSr was produced in a heat-pipe oven and its thermal emission spectrum around 9300 cm−1 was recorded by a high resolution Fourier transform spectrometer. In addition, selected lines of the spectrum of deeply bound vibrational levels of the and states were studied using laser excitation to facilitate the assignment of the lines. The ground state could be described for to 2, up to 105 and the state for up to . For both states, Dunham coefficients, spin–rotation parameters and potential energy curves were evaluated. A coupling of the state to the state was observed, allowing a local description with Dunham coefficients of the state and an approximate evaluation of the coupling strength. (paper)