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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.

Phenol oxidation in a water-oxygen fluid in a tubular batch reactor with its uniform heating (1°C/min) to 600°C was studied. An increase in the amount of O₂ over the stoichiometric ratio by 25% leads to an increase in the degree of carbon burnout by the factor of 1.09. Replacing 10% of the stoichiometric amount of oxygen with nitrous oxide leads to the same increase in the degree of carbon burnout, primarily due to its afterburning at a temperature of ≥ 400°C. Replacement of some part of phenol with isopropanol leads to an increase in the degree of carbon burnout by 1.02 times. It was established for the first time that the heterogeneous mechanism of phenol oxidation in a water-oxygen fluid is the main one. However, the overstoichiometric amount of O₂, as well as the addition of N₂O and isopropanol, intensifies gas-phase combustion of carbon. A catalytic effect of a Pt-Rh/Pt thermocouple on the degree of phenol conversion in the presence of O₂ at temperatures above 135°C was found.

The enthalpy and heat capacity of solid and liquid Mg₂Ca intermetallic alloy were measured with the help of mixing by massive high-temperature isothermal drop calorimeter over the temperature range of 298.15-1177 K. The estimated errors in the data on enthalpy and heat capacity were 0.2% and 2%, respectively. The fusion enthalpy of the Mg₂Ca intermetallic alloy was determined to be 483 ± 3 J/g. The heat capacity of the Mg²Ca melt was shown to be constant in the range of 993.2-1177 K. A comparison of the obtained results with literature data has been carried out.

The presented paper considers a number of problems. The first of them concerns the analysis of experimental (ρ_l, ρ_g, T)-data for SF₆ at relative temperatures (1,5∙10^-8< τ < 0,3). The second task is related to the development of combined models (ρ_l(D, C, τ), ρ_g( D, C, τ), … ), that agree with a number of boundary conditions, including the requirements of the scale theory of critical phenomena. The third task is to calculate (D, C)-parameters included in the combined models; at this stage, a basic array of (ρ_l, ρ_g, T)-data is formed, including experimental results obtained in the laboratory of Prof. Funke (Germany), and (ρ_l, ρ_g, T)-data obtained by recalculating the results in the laboratory of Prof. Garrabos (France). The models for (ρ_l(D, C, τ) and ρ_g(D, C, τ) served as the basis for calculating some thermodynamic properties of SF₆ in the critical region.

Using the method of differential scanning calorimetry, the heat capacity of Mg-Ca alloys containing 10.50, 33.34, and 73.00 at. % Ca, being promising for various practical applications (biocompatible and biodegradable alloys, ultralight construction materials, anode materials, hydrogen absorbent materials, etc.) has been studied experimentally. New reliable experimental results on the specific heat capacity in the temperature range of 190-576.692 K of the solid state have been obtained. The estimated errors of the received data were 2-3 %. The reference tables for temperature dependences of specific heat capacity of Mg-Ca alloys have been compiled. It has been established that over a wide temperature range the heat capacity of solid magnesium-calcium alloys can be estimated with high accuracy using the Neumann-Kopp rule.

The paper describes an algorithm that using numerical methods allows calculating the relationship between the temperature of the spectral ratio and the actual temperature of a "non-gray" object, which takes into account not only the dependence of the spectral emissivity of the object on the wavelength, but also its temperature dependence, inherent in almost all real objects (materials). This algorithm is applicable to any pyrometers of spectral ratio: narrowband and broadband ones. Previously, both in domestic and foreign literature, there has been no solution to the specified problem which would simultaneously consider both dependences. The proposed solution is based on a well-known algorithm that allows calculating the relationship between the temperature of the spectral ratio and the actual temperature of a "non-gray" object, taking account only the dependence of the spectral emissivity of the object on the wavelength. The presented algorithm has been modified to consider its temperature dependence as well. An example of the implementation of the described algorithm is given.

The results of an experimental study of the thermal expansion of gallium garnets Gd₃Ga₅O₁₂, Gd_3.04Sc_1.8Ga_3.16O₁₂ and Ca₃Nb_1.5Ga_3.5O₁₂ in a wide temperature range (293.15 - 1473 K) are presented. A noticeable effect of niobium in the structure of gallium garnets on the coefficient of thermal expansion has been found. The temperature dependences of the volumetric properties have been obtained.

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.