Random mode coupling assists Kerr beam self-cleaning in a graded-index multimode optical fiber

In this paper, we numerically investigate the process of beam self-cleaning in a graded-index multimode optical fiber, by using the coupled-mode model. We introduce various models of random linear coupling between spatial modes, including coupling between all modes, or only between degenerate ones, and investigate the effects of random mode coupling on the beam self-cleaning process. The results of numerical investigations are in complete agreement with our experimental data

Beam self-cleaning in multimode optical fibers and hydrodynamic 2D turbulence

We experimentally demonstrate the conservation of the average mode number in the process of Kerr beam self-cleaning in a graded-index multimode optical fiber, in analogy with wave condensation in hydrodynamic 2D turbulence

Mode decomposition method for investigating the nonlinear dynamics of a multimode beam

We overview our recent experimental studies on the nonlinear spatial reshaping of multimode beams at the output of multimode optical fibers. We use a holographic mode decomposition technique, which permits to reveal the variation of the spatial mode composition at the fiber output, as determined by either conservative (the Kerr effect) or dissipative (Raman scattering) nonlinear processes. For the first case, we consider the effect of spatial beam self-cleaning, and we compare experimental mode decompositions with predictions based on the thermodynamic theory, including the case of beams carrying nozero orbital angular momentum. For the second case, we analyze the beam mode content at the output of a Raman laser based on a graded index multimode fiber

Hydrodynamic 2D Turbulence and Spatial Beam Condensation in Multimode Optical Fibers

We show that Kerr beam self-cleaning results from parametric mode mixing instabilities that generate a number of nonlinearly interacting modes with randomized phases - optical wave turbulence, followed by a direct and inverse cascade towards high mode numbers and condensation into the fundamental mode, respectively. This optical self-organization effect is an analogue to wave condensation that is well known in hydrodynamic 2D turbulence

High-Resolution Bitter Decoration Technique for Low Temperatures

We present the high-resolution technique to visualize magnetic flux structure of super-conductors and magnets at low temperatures. The method is based on magnetic nanoparticles preparation in situ low-temperature experiment by magnetic matter evaporation over sample surface in helium atmosphere

Investigation the structure and properties of deformed semi-finished products produced from chips of Al–Mg alloys system alloyed with scandium

The article presents the results of studies that make it possible to solve the problem of processing secondary waste from expensive aluminum alloys without irretrievable loss of metal. For this purpose, tasks were set and solved for the development of technological schemes for obtaining longish deformed semi-finished products from chip waste of Al–Mg alloys 01570 and 1580 alloyed with scandium using methods of powder metallurgy and metal forming. For their experimental verification, the operations of chip briquetting, combined rolling-extrusion (continuous extrusion), sectional rolling, hot extrusion and drawing in combination with heat treatment were applied. According to these schemes, semi-finished products in the form of rods and wires were obtained. Structure and mechanical properties were investigated. It has been revealed that when hot-extruded rods are obtained from chip briquettes of alloy 01570 on a vertical hydraulic press, even with significant degrees of deformation during extrusion, the margin of plastic properties is small and makes it possible to obtain a wire with a diameter of only 4.2 mm after drawing. The processing of briquettes from 1580 alloy chips using the combined rolling-extrusion method makes it possible to obtain after cold deformation a wire with a diameter of up to 3 mm. At the same time, the influence of the annealing process on the structure and properties of deformed semi-finished products from the investigated alloys was studied. It is shown that due to the low plasticity of the investigated material cold working of the rods must be carried out with small degrees of deformation, alternating it with intermediate annealing according to the proposed regime. An analysis of the physical and mechanical properties of the wire obtained using combined processing showed that its strength and plastic properties are comparable to the properties of the wire obtained from a cast billet, and the structure is characterized by a high degree of elaboration and compactness. Thus, as a result of the research, technological schemes have been developed and processing parameters have been determined for the production of rods and wire from graded chip waste of alloys 01570 and 1580 using compaction, discrete and continuous extrusion, as well as cold drawing. © 2022 The AuthorsMinistry of Education and Science of the Russian Federation, Minobrnauka: FSRZ-2020-0013The research was carried out within the framework of the state assignment of the Ministry of Science and Higher Education of the Russian Federation (scientific theme code FSRZ-2020-0013)

РАСЧЕТНО-ЭКСПЕРИМЕНТАЛЬНАЯ ОЦЕНКА УСЛОВИЯ РЕАЛИЗАЦИИ ПРОЦЕССА СОВМЕЩЕННОЙ ПРОКАТКИ-ПРЕССОВАНИЯ С ИСПОЛЬЗОВАНИЕМ МЕТОДА БАЛАНСА МОЩНОСТЕЙ

The paper presents the results obtained when solving the problem consisting in determination of the combined extrolling process implementation. The components of a total capacity for the process studied were written in analytical form, their calculation and analysis of the effect of specific factors on implementation of the combined extrolling process was made on PC using a specially developed program. A quantitative evaluation of the process feasibility was made using safety factor as a major criterion for the conditions of aluminum alloy combined extrolling at the pilot combined processing plant.Приведены результаты решения задачи по определению возможности реализации процесса совмещенной прокатки-прессования (СПП). В аналитическом виде записаны составляющие полной мощности для исследуемого процесса, с помощью разработанной программы на ЭВМ произведен их расчет и проанализировано влияние отдельных факторов на осуществление процесса СПП. Для условий совмещенной прокатки-прессования алюминиевых сплавов на опытно-промышленной установке совмещенной обработки дана количественная оценка возможности реализации процесса с использованием в качестве основного критерия коэффициента запаса мощности