Interplay of Kerr and Raman beam cleaning with a multimode microstructure fiber

We experimentally study the competition between Kerr beam self-cleaning and Raman beam cleanup in a multimode air-silica microstructure optical fiber. Kerr beam self-cleaning of the pump is observed for a certain range of input powers only. Raman Stokes beam generation and cleanup lead to both depletion and degradation of beam quality for the pump. The interplay of modal four-wave mixing and Raman scattering in the infrared domain lead to the generation of a multimode supercontinuum ranging from 500 nm up to 1800 nm

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

Self-cleaning on a higher order mode in ytterbium-doped multimode fiber with parabolic profile

We experimentally demonstrate polarization-dependent Kerr spatial beam self-cleaning into the LP11 mode of an Ytterbium-doped multimode optical fiber with parabolic gain and refractive index profiles

Сучасний стан деревних насаджень на контрактовій площі Києва та перспективи їх реконструкції

Contract Square in Kiev is located in the historical part of the city. The area is of great historical and town-planning significance as it is an important traffic interchange of the city. In recent years, the square has been partially transformed into a pedestrian zone. It has been planned to reconstruct the existing greenery due to the planned reconstruction of the square and its transformation into a pedestrian zone. The inventory of the existing greenery was carried out on the order of the designer and in accordance with the requirements of regulatory documents. The analysis of the taxonomic composition and sanitary state of the square dendroflora was carried out based on the results. The analysis has revealed that currently there are 1618 woody plants on the territory of the area, of which 496 trees, are represented by woody plants of 65 species and 24 cultivars, which are united into 41 genus, 23 families and 2 sections. Rosaceae families make the largest number of species – 18 species and 5 ornamental forms; Cupresaceae – 4 types and 7 decorative forms; Pinacea – 5 species and 4 cultivars. Thirty five of 65 species are cultivars of the woody plants, only 16 species are the aboriginal, the rest are alien plants. The sanitary condition of most woody plants is satisfactory, some trees of the Fraxinus lanceolata Borkh, Acer sacharinum March., Robinia pseudoacacia L., Populus balsamifera L. species are invaded with Viscuv album L. parasite and are referred to categories III and IV of the sanitary status. The trees of Aesculus hippocastanum L. have low decorativeness in the second half of the vegetation due to defoliation caused by the leaves damage with Cameraria ohridella Desch. & Dem. (Gracillariidae: Lepidoptera) and are referred to the categories ІІ and ІІІ of sanitary status. Trees of category V and VI sanitary status were not found on the territory of the area. The greatest taxonomic diversity is typical for the dendroflora of the park located to the south of the building of the shopping arcade, where the monument to Hetman Sahaidachnyi was erected in 2001. 624 woody plants grow here including 192 trees; the rest is represented by bushes of 34 species and decorative forms and belong to 28 genera and 18 families. The basis of tree group compositions is made up by the trees whose age exceeds 50 years, among which Gymnoclodus dioica (L.) K. Koch., aged over 70, as well as mighty trees of Acer sacharinum, Robinia pseudoacacia, Fraxinus lanceolata, Aesculus hippocastanum. They are successfully supplemented with 30 and 40-year old evergreen Picea pungens trees, as well as bushes of Taxus bacata, Juniperus sabina, J. communis, Tuja ocidentalis 'Smaragd', aged under 20. It should be noted that the hedging Tuja ocidentalis 'Fastigiata' is not a successful designer's idea. There are 155 woody plants including 82 trees and 73 bushes in the garden located on the north of the shopping arcade. The bushes are represented by three species and the trees – by ten ones. The largest number of specimen includes Tillia platifylos and Fraxinus lanceolata – 19 plants for each, Tillia cordata is represented by 10 trees, Acer platanoides – by 5, Aesculus hippocastanum – by 4 trees. Several trees of Acer sacharinum and Fraxinus lanceolata are classified in the III category of the sanitary status due to their invasion with the mistletoe white. The trees in the square are somewhat thickened, the grass cover is missing. Dendroflora of the park located in the northern part of the square, next to the underground station numbers 58 trees and 3 shrubs that belong to 10 species, 8 genera and 5 families. The basis of the plantation is composed of species like Fraxinus lanceolata, Robinia pseudoacacia, Ulmus glabra, they are successfully supplemented with Picea pungens and Pinus sylvestris trees planted about 15 years ago. 36 trees of Fraxinus angustifolia 'Raywood', planted in 2017, fit in the landscape successfully. An integrated assessment of the value of plantations carried out in accordance with our own methodology showed that plantings of square 1 (38 points) are valuable, plantations of squares 2 (31) and 3 (32) are of limited value, and roadside plantations along the perimeter of the square, gaining 22 points, are of low value and can be used during the reconstruction only partially. The authors suggest adhering to the following algorithm during the reconstruction: inventory of existing plantings – sanitary felling – landscape felling – replanting new trees and shrubs – carrying out quality care for plants.На основі аналізу результатів інвентаризації деревних насаджень на території Контрактової площі в Києві встановлено, що на площі зростають 1618 дерев та кущів, із них 496 дерева. Дендрофлора складається із 65 видів та 24 культиварів деревних рослин, які об'єднані в 41 рід та 23 родини. Із 65 видів та 25 культиварів деревних рослин тільки 16 видів є аборигенними, решта – інтродуценти. За життєвою формою переважають дерева – 86 % від загальної кількості видів. Найпоширеніші 11 видів дерев, які становлять майже 77 % від загальної кількості рослин. Більшість дерев віднесено до І і ІІ категорій санітарного стану. До ІІІ категорії віднесено ряд дерев, заселених Viscum album L., видів Fraxinus lanceolata Borkh, Acer sacharinum March., Robinia pseudoacacia L., Populus balsamifera L. Деревна рослинність зосереджена у трьох скверах та в придорожніх насадженнях по периметру площі. Найбільшим видовим різноманіттям (34 види) характеризується сквер № 1, що розташований у південній частині площі, а найменшим (10 видів) – сквер № 3, розташований у північній частині площі. У сквері № 2 виявлено 13 видів деревних рослин. Проведено інтегральне визначення цінності насаджень: насадження у скверах визнано цінними, а в придорожніх насадженнях – малоцінними. Запропоновано алгоритм реконструкції насаджень

Spatial beam self-cleaning and supercontinuum generation with Yb-doped multimode graded-index fiber taper based on accelerating self-imaging and dissipative landscape

We experimentally demonstrate spatial beam self-cleaning and supercontinuum generation in a tapered Ytterbium-doped multimode optical fiber with parabolic core refractive index profile when 1064 nm pulsed beams propagate from wider (122 µm) into smaller (37 µm) diameter. In the passive mode, increasing the input beam peak power above 20 kW leads to a bell-shaped output beam profile. In the active configuration, gain from the pump laser diode permits to combine beam self-cleaning with supercontinuum generation between 520-2600 nm. By taper cut-back, we observed that the dissipative landscape, i.e., a non-monotonic variation of the average beam power along the MMF, leads to modal transitions of self-cleaned beams along the taper length

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

Spatiotemporal Characterization of Supercontinuum Extending from the Visible to the Mid-Infrared in Multimode Graded-Index Optical Fiber

We experimentally demonstrate that pumping a graded-index multimode fiber with sub-ns pulses from a microchip Nd:YAG laser leads to spectrally flat supercontinuum generation with a uniform bell-shaped spatial beam profile extending from the visible to the mid-infrared at 2500\,nm. We study the development of the supercontinuum along the multimode fiber by the cut-back method, which permits us to analyze the competition between the Kerr-induced geometric parametric instability and stimulated Raman scattering. We also performed a spectrally resolved temporal analysis of the supercontinuum emission.Comment: 5 pages 7 figure