Specific mode output from multimode fiber oscillators by designing rare earth doping profiles

Based on rate equations, a theoretical model of a fiber oscillator with a multimode gain fiber was built. We studied the effect of the rare earth doping profile in the core on the output characteristics of the multimode fiber oscillator. The results indicated that a pure fundamental mode can be obtained by partly doping the core of the large mode area （LMA） ytterbium doped fiber （YDF） in the fiber laser. Furthermore, a sole specific high-order mode can also be implemented by tailoring the rare earth doping profile according to the simulations. The mode coupling effect was also taken into account in the model. In spite of the mode coupling effect, the specific mode was able to dominate in the output of the fiber laser by utilizing the designed LMA YDF.

Mode Specificity Dynamics of Prototypical Multi-Channel H+CH_(3)OH Reaction on Globally Accurate Potential Energy Surface

The H+CH_(3) OH reaction,which plays an important role in combustion and the interstellar medium,presents a prototypical system with multiple channels.In this work,mode specific dynamics of different product channels is investigated theoretically on a recently developed reliable potential energy surface based on a large number of data points calculated at the level of UCCSD(T)-F12 a/AVTZ.It has been demonstrated that vibrational excitations of the O-H stretching motion,the torsional motion,the C-H stretching vibrations,show different infuences on the four product channels,H_(2)+CH_(3) O,H_(2)+CH_(2)OH,H_(2) O+CH_(3),and H+CH_(3) OH.This work is helpful for understanding the mode-specific dynamics and controlling the competition for complicated reactions with multiple product channels.

Mode-Specific Quantum Dynamics Study of OH+H_(2)S→H_(2)O+SH Reaction

The hydrogen abstraction reaction from H_(2)S by OH is of key importance in understanding of the causes of acid rain,air pollution,and climate change.In this work,the reaction OH+H_(2)S→H_(2)O+SH is investigated on a recently developed ab initio-based globally accurate potential energy surface by the time-dependent wave packet approach under a reduceddimensional model.This reaction behaves like a barrier-less reaction at low collision energies and like an activated reaction with a well-defined barrier at high collision energies.Exciting either the symmetric or antisymmetric stretching mode of the molecule H_(2)S enhances the reactivity more than exciting the bending mode,which is rationalized by the coupling strength of each normal mode with the reaction coordinate.In addition,the modespecific rate constant shows a remarkable non-Arrhenius temperature dependence.

Mode-specific and bond-selective dissociative chemisorption of CHD_3 and CH_2D_2 on Ni(111) revisited using a new potential energy surface

Dissociative chemisorption of methane on a nickel surface is a prototypical system for studying mode-specific chemistry in gassurface reactions.We recently developed a fifteen-dimensional potential energy surface for this system which has proven to be chemically accurate in reproducing the measured absolute dissociative sticking probabilities of CHD_3in thermal conditions and with vibrational excitation on Ni(111)at high incident energies.Here,using this new potential energy surface,we explored mode specificity and bond selectivity for CHD_3and CH_2D_2dissociative chemisorption at low incidence energies down to^50 k J/mol via a quasi-classical trajectory method.Our calculated dissociation probabilities are consistent with previous theoretical and experimental ones with an average shift in translational energy of^8 k J/mol.Our results very well reproduce the C–H/C–D branching ratio upon the C–H local mode excitation,which can be rationalized by the sudden vector projection model.Quantitatively,however,the calculated dissociative sticking probabilities are systematically larger than experimental ones,due presumably to the artificial zero point energy leakage into reaction coordinate.Further high-dimensional quantum dynamics calculations are necessary for acquiring a chemically accurate description of methane dissociative chemisorption at low incident energies.

First principles study and comparison of vibrational and thermodynamic properties of XBi(X=In,Ga,B,Al)

In the present work, vibrational and thermodynamic properties of XBi（X = B, Al, Ga, In） compounds are compared and investigated. The calculation is carried out using density functional theory（DFT） within the generalized gradient approximation（GGA） in a plane wave basis, with ultrasoft pseudopotentials. The lattice dynamical properties are calculated using density functional perturbation theory（DFPT） as implemented in Quantum ESPRESSO（QE） code. Thermodynamic properties involving phonon density of states（DOS） and specific heat at constant volume are investigated using quasiharmonic approximation（QHA） package within QE. The phonon dispersion diagrams for InBi, GaBi, BBi, and AlBi indicate that there is no imaginary phonon frequency in the entire Brillouin zone, which proves the dynamical stability of these materials. BBi has the highest thermal conductivity and InBi has the lowest thermal conductivity. AlBi has the largest and GaBi has the smallest reststrahlen band which somehow suggests the polar property of XBi materials. The phonon gaps for InBi, GaBi, BBi and AlBi are about 160 cm^-1, 150 cm^-1, 300 cm^-1, and 150 cm^-1, respectively. For all compounds,the three acoustic modes near the gamma point have a linear behavior. C_V is a function of T-3 at low temperatures while for higher temperatures it asymptotically tends to a constant as expected.

Comprehensive Investigations of the Cl+CH_(3)OH→HCl+CH_(3)O/CH_(2)OH Reaction:Validation of Experiment and Dynamic Insights

Cl+CH_(3)OH→HCl+CH_(3)O/CH_(2)OH is a prototypical multiple-channel reaction.Experimentally,ample dynamical and kinetic information is available,but there are still many uncertainties concerning the reaction mechanism.Theoretical investigations are rare due to the absence of a potential energy surface(PES),which has greatly hindered our understanding of the reaction dynamics.Using a machine-learning approach,an accurate full-dimensional PES for the title reaction based on tens of thousands of high-level ab initio data is reported.Comprehensive dynamical calculations were performed on the PES using quasi-classical trajectories,and the results provide insights into the reaction kinetics and dynamics.The calculated non-Arrhenius rate coefficients are consistent with the experimental data,attributable to a complex-forming mechanism at low temperatures.At high energies,the reaction is dominated by a direct mechanism,which results in dominant forward scattering via a stripping mechanism augmented by less prominent sideways and backward scattering via a rebound mechanism.At collision energies of 5.6 and 8.7 kcal/mol,the measured product translational energy and ro-vibrational state distributions of HCl are well reproduced.In addition,mode specificity is revealed and rationalized by the sudden vector projection model.This work sheds valuable light on the microscopic mechanism and dynamics of this prototypical multichannel reaction.