For the porous carbon material excited by the first and second harmonics of a neodymium laser, the shape of pulsed signals of laser-induced thermal emission is investigated. It is found that the duration of thermal emission pulses significantly depends on the wavelength of the laser excitation, which is caused by the differences in the depth of penetration of laser radiation into the surface layer. The mentioned effect is actual, if the penetration depth of laser radiation exceeds the length of thermal diffusion in the studied material for a time of the order of the laser pulse duration. The computer modeling is carried out for the processes of pulsed laser heating and formation of thermal emission signal. The simulation results showed satisfactory agreement with the measurement results.

The influence of the surrounding air on the amplitude and shape of thermal radiation pulses (at a wavelength of 430 nm) during the heating of the surface layer of a porous carbon material (to temperatures of the order of 2000-3000 K) by the radiation of a Q-switched neodymium laser is studied. When the pressure of the surrounding air is reduced to forevacuum conditions, the experiments showed a one-and-a-half-fold increase in the amplitude of pulsed signals of thermal radiation and an increase in the decay time of the glow by about a third. Numerical calculations of the dynamics of the temperature field in the surface layer of the material during the irradiation by nanosecond laser pulses are carried out. An improved model is used in the calculations, which accounts for (i) the porosity of the material and (ii) the temperature dependence of the coefficients of thermal conductivity and the heat capacities of carbon and air. To calculate the thermal conductivity of the porous material, a model of a cubic array of intersecting square rods is used. The satisfactory consistency of calculation results with experimental data is obtained. The above-mentioned improvements of the calculation model made it possible to reconcile the estimates of the thermal characteristics of surface layers of carbon, obtained from the emission decay data, with the reference data published in the literature.

Thermal emission is an informative tool to study materials’ properties at high temperatures under laser irradiation. The kinetics decay of laser-induced thermal emission from carbon microparticles deposited on heat-sink surfaces of transparent dielectrics (glass and sapphire) was studied. A Q-switched YAG:Nd3+ laser (pulse duration τi = 20 ns, energy/power density 0.5 J·cm–2, 25 MW·cm–2) was employed to excite thermal emission. In calculations, the classical heat conduction equation was used. With increasing the thermal conductivity of substrate (from glass to sapphire), reduction in the emission pulse duration has been observed.

Computer simulation is performed for pulsed laser heating of a surface with submicrometer-sized truncated-cone-shaped peaks and holes. Transient temperature field is calculated, and the visual appearance of the surface roughness elements is modeled with the laser-induced thermal emission. The results of calculations reveal special features in visual appearance of peaks on the surface which opens a possibility to distinguish between different surface elements. The calculations also predict 20 fold variations of local thermal emission radiant exitance of rough surfaces. The experiments confirm the presence of the exitance variations on rough surfaces of carbon materials.

The decay of thermal emission of rough surface layers of different carbon materials under the pulsed laser excitation is analyzed both theoretically and experimentally. For pulsed laser heating of rough surfaces, computer simulations revealed that laser-induced thermal radiation is mainly emitted by peaks of the surface relief, and the emission decay time depends on the relation between the laser penetration depth and the temperature diffusion length. It is also concluded that the presence of surface roughness can significantly increase the emission decay time. In the experiments, carbon materials with different thermal characteristics were used; however, all of the investigated samples demonstrated close values of the emission decay time. This fact shows that the material's characteristics on the peaks of surface relief are similar for different carbon materials at high temperature.

The decay of thermal radiation emitted by surface layers of carbon materials excited by pulses of a Q-switched neodymium laser is investigated experimentally and theoretically. It is discovered that the decay curves can be approximated with satisfactory accuracy by a sum of two exponential components with decay times of about 10 and 100 ns. Changes in the decay curves under sample irradiation by a sequence of laser pulses can be interpreted as being the result of redistribution of intensities of these two components. Based on the results of computer simulation, the conclusion is drawn that the glow-decay time is determined by the ratio of the penetration depth of the laser radiation and the thermal-diffusion length, which creates an opportunity to determine the coefficient of temperature conductivity in a thin surface layer of the studied material at high temperatures (thousands of Kelvins).

Channels of the 137Cs and potassium transfer from soil to plants in the field under water-stressed conditions are investigated. Different rapidly maturing plants were grown and selected simultaneously several times during the 2012 and 2013 seasons at the same experimental sites with different soil types under natural conditions at the Chornobyl 10-km Exclusion Zone. After each selection, the contents of 137Cs and K in the plants and extracted soil solutions were measured. Potassium and cesium entered plant roots, as a rule, through transporters with low selectivity, when the concentration of dissolved potassium (CK) in soil was greater than 2 /ug/cm3. In this case, the selectivity of the plant uptake for 137Cs versus potassium r was near 1. However, when CK was between 0.5 and 2 /ug/cm3, potassium also appeared to enter plant roots through highly selective potassium transporters, while cesium entered roots only through the transporters with low selectivity. In this case, the value of r was much less than 1. When CK was less than 0.5 /ug/cm3, cesium and potassium appeared to enter roots through a complement of transporters with greater selectivity for cesium than for potassium. The value of r in this case could exceed 1.

For porous carbon samples made of bio-materials (nutshells) by pyrolysis, laser-induced incandescence is investigated under irradiation by a sequence of pulses of a Q-switched YAG:Nd laser. For the intensity of LII as a function of the laser irradiation dose, two- or threestage kinetics is observed depending on the incident laser intensity. Physical mechanisms of the observed increase and decrease of LII with the irradiation dose are discussed. The mechanisms include transformations of structure of the irradiated surface layer due to the vaporization of carbon. Besides, the effect of heating of the whole sample on the intensity of LII is also considered.

Concentrations of Cs-137 and potassium in solutions extracted by centrifugation from soils selected at some experimental sites in the 10-km Exclusion Zone of Chornobyl Nuclear Plant were determined. The results showed that for the majority of investigated soils, the concentration of Cs-137 in soil solution depends on the humidity of the soil before centrifugation. It is possible to explain the dependence of the concentration of Cs-137 in the soil solution on soil humidity from the dependence of the concentrations of molecules of different molecular-gravimetric fractions in soil solution on soil humidity. Considerable amount of Cs-137 in soil solution is associated with these molecules, that is why the concentration of Cs-137 in the extracted soil solution changes with the humidity of soil. These dependences differ between soils. For the majority of investigated soils the concentration of Cs-137 in the extracted soil solution increases with increasing humidity of the soil. By contrast, soil humidity had no effect on the potassium concentration in the extracted soil solution for any soil investigated. It is concluded, that potassium is practically not associated with molecules of different molecular-gravimetric fractions in the extracted soil solutions.

Irradiation of light-absorbing porous carbon by pulses of a Q-switched YAG:Nd 3+ laser ( λ = 1064 nm, τ = 20 ns, power density of 3-30 MW/cm 2 ) leads to its heating up to temperatures of several thousands of Kelvin which results in pore expansion in the undersurface region and is accompanied by thermal emission. The effect of laser-induced pore expansion on thermal emission (a.k.a. laser-induced incandescence, LII) with an increase in laser irradiation dose was studied. The experimental results and calculation data demonstrate a significant impact of undersurface pore expansion and carbon evaporation on the LII behavior.

We performed a comparative analysis of photoluminescence spectra of micro- and meso-fractions of powdery ZnS:Mn obtained by self-propagating high-temperature synthesis. It was found that manganese ions take part in excitation of ZnS self-activated luminescence. From the data on photoluminescence excitation spectra it was established that excitation of emitting Mn ion in ZnS:Mn meso-fraction is realized with participation of sensitizers (MnZn) and without charge carriers excited at interband absorption. This is explained within a model according to which, at particles size smaller than double length of the space charge region, the particle potential barrier becomes lower and Fermi level decreases owing to summation of space charge regions of opposite particle surfaces, i.e., the depletion region extends over the total particle volume.

Interaction of highly viscous polystyrene suspensions of light-absorbing microparticles with pulsed radiation of a Q-switched YAG:Nd3+ laser is investigated. Absorption of laser radiation by the suspended microparticles causes thermal decomposition (pyrolysis) of the polymer in the vicinity of the overheated particles. Laser-induced incandescence (LII) of light-absorbing microparticles under irradiation by a sequence of laser pulses is observed. The mechanism of laser marking includes formation of light-absorbing and scattering centers by accumulation of carbonaceous and gaseous products of pyrolysis.

Laser-induced incandescence (LII) of silicon surface is investigated under the excitation by a Q-switched YAG:Nd laser. With the increase of laser irradiation dose, the increase of LII signal is observed, which is attended by visible changes of the surface geometry. The anomalous behavior of the parameter of non-linearity of LII is observed with the increase of laser excitation power.

The relaxation kinetics of laser-induced scattering and absorption was investigated in a liquid epoxy resin suspension of carbon microparticles. The scattered light intensity and the optical transmittance at temperatures below +10°C demonstrate anomalous kinetics with a distinct build-up stage. The observed behavior is interpreted as a manifestation of processes of mechanical stress relaxation in epoxy layers around microbubbles. The microbubbles induced by laser irradiation of the suspension can be a tool for the investigation of mechanical stress relaxation in polymers.

A method of synthesis of alkali-borate glass activated with carbon microparticles is proposed. The behavior of thermal emission of carbon microparticles in the glass under excitation by a Q-switched neodymium laser is investigated. With the increase of laser irradiation dose, the fading of laser-induced emission observed in experiment is interpreted to be due to the carbon particle size reduction caused by the laser irradiation.

A method for preparing aqueous electrolyte solutions of nonsoluble tin-and lead-based compounds has been developed. It is based on the underwater laser ablation stimulated by a neodymium Q-switched laser. Absorption and luminescence spectra of the solutions obtained have been studied.

The conductance and the current-voltage characteristics of metallic single wall carbon nanotube bundles have been measured between 4.2 and 330 K using 10–30 ns electric pulses to avoid overheating. The current-voltage characteristics at different temperatures collapse to a single curve when plotted in the specific coordinates following from the Tomonaga–Luttinger (T–L) liquid concept. Direct evidence is obtained for the existence of a T–L liquid phase up to 190 K and the system shows a transition between the T–L liquid state and a Mott insulating phase below 25 K.

The effect of optical limiting is investigated in the suspensions of carbon microparticles in aqueous gelatin gel and epoxy resin. Both transient and permanent changes of optical transmittance are observed after the irradiation by a Q-switched YAG:Nd3+ laser pulses. The experimental results are explained with taking into account the formation of micro-bubbles filled with water steam and with gaseous products of decomposition of the matrix. In the epoxy resin suspensions, the laser-induced permanent changes of transmittance are caused by pyrolysis of epoxy oligomers in the vicinity of laser-heated carbon particles.

Laser-induced incandescence (LII) of carbon microparticle suspensions in high-viscosity media under powerful excitation with a Q-switched neodymium laser has been investigated. The effect of LII buildup was detected, when suspensions of synthetic resins and polymers were irradiated with a sequence of laser pulses. The experimental data testify to an increase of the effective size of emission centers under the action of the laser radiation.

The optical absorption and the luminescence spectra of aqueous solutions of thallium (I) are investigated. The solutions were produced by means of underwater laser ablation of thallium (III) oxide. The laser ablation is investigated both with and without presence of chlorine ions in the solution. The formation of thallium complexes with chlorine ions is verified by the measurements of UV absorption and luminescence spectra.