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We review our development of wavelength tuneable, high average power, picosecond-pulse, mid- infrared sources in the three micron widow for proposed application in tissue ablation studies and with the objective of source simplification and exploring the potential of all-fiber integration. Initial systems were based on difference frequency generation (DFG) of two synchronous master oscillator power fiber amplifier (MOPFA) schemes. The generated idler was tuneable over the range 3.28-3.45 µm, delivering greater than 3 W of average power, with a maximum pump to total DFG power conversion efficiency of 78 %. By simplifying the seed sources through synchronised in-line modulation of cw diode laser sources, more than 6 W was generated 3.31-3.48 µm with similar efficiency and with near diffraction limited beam quality (M2 = 1.4). In an improved and significantly simplified experimental configuration a source emitting around 3 µm was developed employing a novel χ⁽³⁾/χ⁽²⁾ cascaded nonlinear conversion architecture. Picosecond pulses from a 1.064 µm mode-locked Yb:fiber pump laser were used to generate 1.65 µm signal pulses through χ⁽³⁾ based four-wave mixing in a polarisation preserving photonic crystal fiber (PCF). The output of the PCF was then directly focused into a periodically poled lithium niobate crystal, generating idler radiation around 3 µm, with peak powers of ̴ 0.5 kW, via χ⁽²⁾-based three-wave mixing between the pump and signal pulses.

Nonlinear optics in multimode fibers (MMFs) has had a renaissance over the past two decades, driven by both basic and applied research. MMFs provide an ideal setting for studying multidimensional systems with their complicated collective dynamics. The uniqueness of MMF including the spatial degree of freedom, spatiotemporal dynamics, and inherent disorder make them an ideal tool for exploring novel physics beyond communication. Here, we briefly discuss an overview of nonlinear dynamics in MMFs by focusing their applications in spatiotemporal pulse shaping, self-beam cleaning, and broadband continuum generation. The nonlinearities in MMFs can be useful in linear and nonlinear imaging in microscopy and endoscopy configurations. The growing interest among researchers for nonlinearity in MMFs fibers is pretty evident, indicating a growth in the value of MMFs.

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 us 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.

We experimentally and numerically demonstrate the inability for picosecond telecom pulses to form a single multimode soliton in a graded-index fiber. This property is useful in space-division multiplexed systems, to transmit independent soliton channels which do not merge into a single multimode soliton.

Here we present the results of thermodynamic and kinetic calculations as well as experimental studies of plasma processing of rubber powder of recycled tires, demonstrating the promise of using the plasma-chemical technology for gasification of this powder with the production of energy gas. The results of experiment and calculations were compared and showed good agreement.

The morphology and mineral composition of cryogenic formations of the Malaya Nizhneudinskaya Cave have been studied by electron microscopy and X-ray powder diffraction. This cave is confined to permafrost. The temperature in the cave is near zero all year round, as a result of which ice formations are widely developed in the cave. When solution freezes, and the subsequent partial evaporation of ice occurs, a cryogenic residue composed of gypsum, calcite, and a rare mineral rapidcreekite Ca₂(SO₄)(CO₃)·4H₂O is formed. Rapidcreekite forms radial-radiant aggregates of acicular crystals of up to 200 μm in length. In our opinion, the source of sulfur is represented by the locally developed interlayers of gypsum in the non-karsting rocks overlaying the limestones. This is the second finding of rapidcreekite in the speleo-cryomineralogenesis environment in the world and the first discovery of this mineral in the caves in Russia.

Erosion plays an important role in removing permafrost degradation products. In order to identify the rates and mechanisms of erosion in degrading permafrost, fluvial landforms in small catchments at the foothills of the Kharaulakh Range were typified, and their morphology, formation conditions, and dynamics for 2019-2022 were characterized. The most dynamic landforms associated with melting ice wedges were thermokarst runoff troughs (water tracks), rills, and thermoerosional gullies. Thermoerosional gullies forming in sediments without wedged ice grow upon very high floods; in the rest of the time, their sides slowly slide down under the action of snowfields. Sediments from gullies and rills are deposited in the upper reaches of small rivers. The channels of small rivers are relatively stable, which is also typical of other permafrost regions. Differences in the dynamics of erosional landforms can be explained by an increase in the thermal rather than mechanical impact of water on frozen deposits, which is observed with the rise in air temperature against the background of relatively stable precipitation in the north of Yakutia.

The elaborated method of regional calculation of the hydrological regime of glaciation includes determination of long-term changes in glacial runoff and glacial feeding in river basins. For the Rhone River basin, monitoring data on glaciation parameters over the period of 1971-2016 and long-term data on precipitation and air temperature at weather stations of Switzerland were used for hydrological and glaciological calculations. The results of linear extrapolation of spatiotemporal changes in the altitude-area characteristics of the classified groups of glaciers proved to be sufficient for calculating the hydrological regime of glaciation. An adequate description of seasonal and long-term glacial feeding of rivers should take into account spatiotemporal variations in the ablation of glaciers depending on the five types of active glacier surface and their altitude-area characteristics. Satisfactory absolute and relative estimates of differences between the measured runoff and the amount of precipitation, evaporation, and glacial feeding in the upper Rhone River in 1971-2010 (Porte du Scex gauging station), as well as between the measured and calculated annual precipitation in the Rhone River basin for 1971-2016, were obtained.

The reasons and conditions for the formation and change of moulins are considered on the base of author’s own data and on published data. Moulins can form above the water level in crevasses in the ice column and cannot form below the water level. The cylindrical shape of moulins is associated with the spraying of water jets at a certain depth from glacier surface. Questions related to different mechanisms of moulin formation, their depth, age, water level fluctuations are considered. A possible connection between moulins and the internal drainage system of glaciers is shown. Since there are glaciers in which water does not penetrate to the bed through moulins, the question of the connection between moulins and thrusts in the ice thickness is being considered.

Changes in the Earth’s insolation by latitudes and seasons in certain periods of the Holocene are considered. A comparative analysis of insolation in boundary years of Holocene geochronological periods with modern insolation (2022) is carried out. The change in summer insolation in the hemispheres is analyzed separately. Quantitative estimates in the intensity of insolation’s changes in the Holocene are assessed with respect to the modern insolation. The extremes of summer insolation in the Northern hemisphere are synchronized with the global paleogeographic events of the Holocene: the transition from the cold Pleistocene epoch to the warm Holocene and the Little Ice Age. Characteristics of the Earth’s orbital motion have also been shown to control the Northern hemisphere summer insolation’s change, which is a factor of the noted global paleogeographic events.