Optimization of Yb-Er microchip laser parameters

Output parameters of microchip lasers based on Yb:Er co-doped phosphate glasses have been numerically calculated using a simplified 4-level model in order to optimize the Yb and Er concentrations and active medium length. It was shown that active media with Yb concentration ~2·10²⁷ m^–3 and length of the order of 1 mm were most appropriate to obtain the practically maximum slope efficiency and minimum threshold power. Simulation results indicated that the Er concentration could be much lower than those currently used in practice. The obtained results were in good agreement with available experimental data.     

Modeling of the exact solution of the inverse scattering problem by functional methods

Relations between different functional algorithms for solving the inverse scattering problem are analyzed. It is shown that the Rose algorithm does not provide a unique solution, but can be used as a means to improve the interference resistance in reconstruction algorithms that provide unique restoration of scatterer characteristics. The possibility of unique reconstruction of refractive-absorbing scatterers by the modified Rose algorithm, which includes the Sokhotsky equation, is illustrated. Results of numeric simulation of the Novikov-Grinevich-Manakov algorithm, which is efficient in reconstructing two-dimensional acoustic refractive-absorbing scatterers of actually arbitrary shape and strength, are presented. The algorithm rigorously allows for multiple scattering effects. It is promising for tomography-like application problems and features a sufficiently high interference resistance.     

Multifrequency generalization of the Novikov algorithm for the two-dimensional inverse scattering problem

The process of reconstruction of two-dimensional refractive-absorbing scatterers by the modified Novikov algorithm is considered. A generalization of this algorithm to the multifrequency mode is proposed. The scattering data obtained at different frequencies are combined in the process of the solution using the a priori known frequency dependence of the scatterer function, which yields the constraint equations that are absent in the single-frequency version. It is shown that the problem of reconstruction instability observed in strong scatterers in the single-frequency mode can be removed by the multifrequency mode. The quality of the scatterer estimate in the multifrequency mode is significantly higher than that of the estimate obtained by straightforwardly averaging the single-frequency solutions. Interference resistance of the algorithm is sufficiently high to allow its application in practice.     

A two-dimensional tomography model for the oceanic inhomogeneity reconstruction with wave and ray representations of acoustic field

A model reconstruction of two-dimensional combined oceanic inhomogeneities (of refractive and kinetic types) in tomographic experiments with ray and wave representations of acoustic field is considered. The possibility of a complete reconstruction of two-dimensional flows from the scattering data alone is illustrated. For the realization of the tomographic scheme, a nonorthogonal redundant basis consisting of a number of intersecting stripes is used. The results of reconstruction are presented for model inhomogeneities of kinetic and combined (refractive-kinetic) types. The iterative reconstruction of the flow velocity vector distribution is considered. The tomographic problem in the ray representation is solved by taking into account both the time delays in the signal propagation along the rays and the ray trajectory distortions due to the inhomogeneity of the medium.     

Reconstruction of acoustic boundary scatterers using the Novikov-Grinevich-Manakov algorithm

Models of perfectly rigid and perfectly soft acoustic scatterers of different dimensions are used to study the applicability limits of the Novikov-Grinevich-Manakov functional algorithm intended for reconstructing two-dimensional scatterers. Particular scattering features intrinsic to boundary scatterers are revealed.     

Model experiments on acoustic tomography of the nonlinear parameter

It is shown experimentally that the scattering of sound by sound can be observed outside the region of interaction between primary waves and that it carries information on the spatial distribution of the scatterer’s nonlinear characteristics. Based on this effect, a simple method for reconstructing the distribution of the nonlinear parameter by using complex-modulated broadband primary signals and a small number of transmit and receive transducers is implemented. The possibility of reconstructing a two-dimensional distribution of a nonlinear parameter inhomogeneity with the use of only three transducers (two transmitters and one receiver) without additional scanning in the aspect angle is demonstrated. This simple scheme loses information on the low-frequency components of the scatterer’s spatial spectrum and reconstructs the distribution of only the spatial variations of the nonlinear parameter.     

Solution of the three-dimensional acoustic inverse scattering problem. The modified Novikov algorithm

For the first time, three-dimensional model scatterers of various strengths and size are numerically reconstructed on the basis of the monochromatic functional-analytical Novikov algorithm. The algorithm allows for the multiple scattering processes and does not impose stringent constraints on the scatterer strength. The resulting scatterer estimate approaches the true value after the width of the scatterer’s spatial spectrum is restricted to a region with a radius of about 2k ₀. The noise robustness of the algorithm, i.e., the robustness to random errors in experimental data, is sufficiently high for diagnostic applications. However, the amount of numerical operations required by the algorithm is great.     

Sensitivity of polarization observables in elastic ed scattering to the neutron form factors

The deuteron elastic form factors are calculated within the Bethe-Salpeter approach with separable interaction. The charge, quadrupole, and magnetic form factors [F _C(q ²), F _Q(q ²), and F _M(q ²), respectively]; the structure functions A(q ²) and B(q ²); and the tensor polarization components T ₂₀(q ², T ₂₁(q ²), and T ₂₂(q ²) are investigated up to ?q ²=50 fm^?2. The role of relativistic effects is discussed, and a comparison with nonrelativistic calculations is performed. The effect of the neutron form factors on the deuteron form factors and especially on tensor polarization components is discussed too.     

Spectral luminescent properties of 2-(2-hydroxyphenyl)-5-methyl-1,3,4-oxadiazole and its acetyl(benzoyl)oxy derivatives

Russian Journal of Organic Chemistry -