Home – Home – Jornals – Atmospheric and Oceanic Optics 2018 number 3

The XIII International Conference on pulsed lasers and their applications AMPL was held in Tomsk in September 10-15, 2017. Subjects of the Conference traditionally enclosed theoretical and experimental studies of physical and chemical processes in laser active media; the newest active media and pumping methods; new laser technologies; fundamental topics of laser physics; application of lasers in science, engineering, medicine, and other spheres; discussion of problems and difficulties in development of laser-based equipment; new optical technologies.

The spectral characteristics of the spontaneous and stimulated luminescence of strongly silicon-doped Al_xGa_1-xN structures with the concentration n_Si > 10²⁰ cm^-3, at the optical pulse pumping by radiation with λ = 266 nm, are studied. The obtained dominant broadband radiation with a full width at half maximum ≈ 150 nm covers the whole visible spectral range. The radiation spectrum from the end of the structure is split into the narrow components determined by the formed flat waveguide mode structure. The results are indicative of the stimulated radiation character. The measured amplification coefficients values for different structures are in the range 20-70 cm^-1.

The switching properties of a new gas-discharge sharpener that consists of “open” and “capillary” discharges serially connected in a bulk are studied. The switching times less than 1 ns have been attained in helium in a wide range of conditions, at times of discharge development delay higher than 600 ns with an initial pulse compression degree of about 10³. An average power of about 10 kW has been implemented in the pulse train mode at a voltage of 20 kV and a pulse frequency of 44 kHz.

The creation of a compact emitter for an inductive nitrogen laser (λ = 337.1 nm) with the active medium pumped by a pulsed inductive longitudinal discharge of the transformer type is reported for the first time. In the inductive laser head created, the lasing energy attains 0.35 mJ and the lasing pulse length is (25 ± 5) ns (FWHM) depending on the resonator Q-factor. The use of a semiconfocal cavity provides for a near-Gaussian beam profile.

Results on quasi-resonant optical pumping of Yb vapors by KrF* laser radiation (λ_p = 248 nm) are presented. The converted radiation is studied in the visible range available for visual observation. Strong lines of amplified spontaneous emission are detected. These lines are due to transitions between the even groups (6s5d ¹D₂, 6s6d ³D_{1, 2, 3}) and odd levels (6s6p ¹P⁰₁, 6s6p ³P_{0, 1, 2}) of ytterbium. Coherent radiation is detected on Yb resonance lines with λ = 398.8 and 555.6 nm, which are caused, respectively, by 6s6p ¹P⁰₁ ® 6s6s ¹S₀ and 6s6p ³P⁰₁ ® 6s6s ¹S₀ transitions in the Yb atom. A sequence of processes that lead to the formation of inversion at the Yb atomic transitions is qualitatively examined.

Electro-physical processes in the discharge circuit of a pulsed metal vapor laser are analyzed. The greatest attention is paid to the initial period of the discharge development and conditions for the inversion formation. It is shown that the limitation of the frequency-energy characteristics (FEC) of lasing is due to the process of population of the metastable levels of metal atoms on the excitation pulse front and redistribution of the rates of population of the laser levels in favor of metastable ones with an increase in the prepulse electron density. Which of the processes plays a decisive role in limiting the lasing FEC depends on the electro-physical process in the discharge circuit of the laser, the development of which is significantly influenced by the arrangement of electrodes in the gas-discharge tube (GDT). The arrangement of the electrodes in the GDT also determines the conditions for the inversion formation and the choice of the optimum pumping parameters. Technical solutions are discussed which allow the copper vapor laser pumping efficiency to attain ~ 10%.

Results of experimental studies of two different-size high-frequency active elements of a CuBr laser operating in generator, single-pass amplification, and superradiance modes are presented. A pulse repetition rate of 195 kHz is attained for the first time in the supperradiance mode. Using the method of express estimation of the radial profile, it is shown that the gain profile does not change significantly throughout a wide pulse repetition rate range (up to 195 kHz) in the case of a small-diameter active element.

Results are presented of the development and study of metal vapors active elements using an induction heater, which is designed to create a required metal vapor concentration. The lasing was obtained at traditional (GDT with internal electrodes) and capacitive (capacitive barrier discharge) excitation of the laser medium; the average laser power was 20 mW. For the Cu-vapor active element under capacitive excitation, two generation pulses with a time delay of 50 ns were detected. Thus, within the limits of a single pump pulse, the lasing was obtained with a frequency of 20 MHz.

It is shown that the use of a power supply with a pulsed step charge of the working capacitance for a CuBr laser excitation allows lasing in the single pulse mode with repetition frequencies from 330 Hz. The effective energy input into the laser medium with operating capacitances from 6.8 to 20.4 nF occurs in 5-11 charge stages. An increase in the pulse lasing energy to 3 mJ is facilitated by increases in the working capacitance and charge voltage.

The process of formation of blue jets in air at low pressures is simulated using the apokamp discharge. The field strength is measured in the discharge channel. Assuming the applicability of rules of similarity for gas discharge, the field intensity in a storm cloud is assessed during the formation of blue jets. The assessments are from 6 × 10¹⁰ to 1.9 × 10⁹ V/m, which is much higher than the values characteristic of the development of cloud-to-ground lightning discharges. A hypothesis is formulated that excess magnitudes of characteristic fields is one of features of high-voltage pulsed discharge within a cloud and causes the formation of blue jets at altitudes of about 12-18 km.

The discharge glow dynamics in a point-plane gap during a nanosecond breakdown of air and nitrogen initiated by runaway electrons is studied with an ICCD camera. Formation of plasma clots that form a structure similar to the even lightning has been observed. It is shown that the number of bright plasma clots in the gap (individual beads) increases with an increase in the pressure. Up to four individual beads of equal size have been recorded in nitrogen at a pressure of 0.4 MPa.

The interaction of iron oxide nanoparticles obtained in acoustoplasma discharge with cavitation with blood plasma fibrinogen is studied in a model solution by dynamic light scattering. Depending on the storage time of the nanoparticles, their interaction with the protein shows different dynamics of the size distribution. However, the biological action of the nanoparticles is the same action regardless of the storage time-they act as inhibitors of the fibrin gel formation reaction.

The paper shows that low-temperature plasma initiated in a liquid medium in the interelectrode discharge gap is capable of decomposing hydrogen-containing organic molecules with formation of gaseous products with the volume part of hydrogen higher than 90% (according to gas chromatography data). Tentative assessments of the energy efficiency with regard for hydrogen and feedstock combustion value and energy consumption have shown an efficiency factor of 60-70% depending on the source mixture composition. Theoretical model calculations of discharge current and voltage have been performed; the values are in a good agreement with experimental data.

Numerical simulation of the processes of heating a vessel with various laser sources (diode, Nd:YAG, CVL, and PDL) to temperatures at which its coagulation can occur is performed. On the basis of the simulation results, the depth and diameters of vessels that can be selectively and safely coagulated are determined, and safe dosage ranges are calculated.

The optical characteristics of water in the stratified lakes of the White Sea are of particular interest in connection with the observation of thin colored layers around chemocline resulting from massive development of anoxygenic phototrophic bacteria. While the chlorophyll optical properties are widely used in remote sensing, the spectral characteristics of bacteriochlorophylls (BChl) for natural microbial communities have been little studied. Spectral study of green sulfur bacteria of four water bodies of the Kandalaksha Gulf of the White Sea was carried out in the work. Absorption and fluorescence spectra were measured for water sampled in March 2017 from various depths and compared with spectra of monocultures isolated from the same reservoirs earlier. It was shown that the fluorescence of BChl in the living cells of green sulfur bacteria has two overlapping emission bands: in the region 740-770 nm (BChl d and e) and at 815 nm (BChl a). The wavelength of maximum of the first band depends on the ratio of the concentrations of green-colored and brown-colored forms of bacteria containing different types of BChl. The new method for determination of contributions of two types of bacteria is proposed, based on the deconvolution of fluorescence spectrum into three bands which parameters were determined from the spectra of monocultures. The BChl content at various water depths was estimated and the percentage ratio of different types of phototrophic bacteria was determined.

The absorption spectra of drinking water, melt water from snow, and heavy water during irradiated by nanosecond electron flux are studied. Under repeated irradiation of water, a change in the absorption spectrum of a substance was observed. The a analysis of water absorption spectra in the IR range showed differences between the absorption spectra of irradiated and non-irradiated water.