Home – Home – Jornals – Atmospheric and Oceanic Optics 2024 number 4

The development of laser technologies leads to high requirements for lasers being developed which generate narrow-band radiation with different wavelengths. In view of this, the importance of wavelength-tunable diode and vibronic lasers with broadband amplification circuits increases. The possibility of generating highly coherent radiation in a solid-state alexandrite laser using an original composite resonator which includes an additional external dispersive resonator has been demonstrated. The results of experimental studies of conditions for the generation of narrow-band (less than 20 pm) radiation in such a resonator with the possibility of smooth tuning of the lasing wavelength in the spectral range 740-780 nm are presented. Narrow-band lasing in an alexandrite laser with a radiation energy of 30 mJ and a pulse duration of 35 ns was demonstrated. The created compact narrow-band alexandrite laser can be an effective alternative to parametric oscillators (OPO) and Ti:Sapphire lasers in lidar systems operating in the spectral range 700-850 nm.

Laser radiation in the yellow wavelength range is widely used in ophthalmology due to its effectiveness and unique properties. Commercial medical laser systems existing today have low pulse power and other disadvantages. A yellow neon laser with a wavelength of 585.3 nm can be proposed as an alternative. This paper describes the experimental study of a neon laser pumped by a pulsed inductive longitudinal discharge. A Ne-H₂ gas mixture with various ratios is used as the active medium. The shape and duration of the lasing pulses strongly depend on the ratio Ne : H₂, providing both single and double pulses with a total duration of 30 to 100 ns (FWHM). The generation energy reaches 20 mJ, which corresponds to a pulse power of 200 W. The cross-section of the laser beam has a shape close to a circle, with a divergence less than 2 mrad. Further, with implementing a pulse-periodic operating mode of an induction neon laser with a pulse repetition rate of up to 100 Hz, it can be used for various applications, including in medicine.

Electric discharge nitrogen lasers remain popular sources of UV radiation and find many scientific and practical applications. Currently, some of the requirements for commercial nitrogen lasers are small overall dimensions, high pulse-to-pulse stability, and extended service life. In this paper, a nitrogen laser excited by a pulsed longitudinal inductive-electric discharge is suggested as a source which satisfies such criteria. As a result of the experimental studies, lasing at wavelengths l₁ = 337.1 and l₂ = 357.7 nm was obtained. The generation energy reached 0.67 mJ with a pulse duration of 20 ns (FWHM) and a nitrogen pressure of 7...8 Torr. Pumping nitrogen only with a longitudinal discharge in an experimental setup with similar parameters led to a decrease in the lasing energy to 0.4 mJ (with the same pulse duration of 20 ns) at a nitrogen pressure of no higher than 5 Torr. Nitrogen lasers with these radiation parameters can be used to treat ophthalmic diseases and tuberculosis.

In the course of technological development of society, the problem of violation of the ecological state of the environment inevitably arises, in particular in water reservoirs. In order to proper respond to the changes in the concentrations of various pollutants in natural water reservoirs, it is necessary to develop an express remote method. The creation of such a method is possible on the basis of Raman spectroscopy. However, during its development, a large number of various difficulties arise, in particular regarding the method of preprocessing the obtained data. The paper presents the results of using machine learning methods to develop a remote method for determining the type and concentration of dissolved ions in aqueous media from Raman spectra. The use of artificial neural networks made it possible to identify and simultaneously determine the concentration of each of the eight ions (Zn²⁺, Cu²⁺, Li⁺, Fe³⁺, Ni²⁺, NH₄⁺, SO₄², and NO₃^-) in a multicomponent aqueous mixture with errors, which meet the needs of environmental monitoring of natural and waste waters. A significant influence of the method of preprocessing Raman spectra on the result of solving the inverse spectroscopic problem is discovered. The results can be used for solution of the multiparameter inverse problem of qualitative and quantitative determination of ions in water.

The glow of diffuse plasma jets (DPJ) is studied, which make it possible to simulate in low-pressure atmospheric air some properties of red sprites - pulsed discharges observed in the upper layers of the Earth's atmosphere at altitudes of 40-100 km. DPJs were initiated by the plasma of a pulse-periodic capacitive discharge created in a quartz tube between two external electrodes and propagated simultaneously in opposite directions. To form the DPJs, which moved towards each other, two pairs of ring electrodes were used, installed at a distance of 66 cm. When unipolar voltage pulses from generators were applied to each pair of ring electrodes with a delay of hundreds of nanoseconds, bright areas of luminescence (BAL) similar to those observed in the lower area of the column sprites appeared. It has been established that at a generator voltage of 7 kV, the optimal air pressure for the appearance of BAL is 1-2 Torr. It is shown that BALs arise due to the interaction of streamers that make up the DPJs. The speed of propagation of the DPJ front was measured for the positive polarity of voltage pulses applied to the ring electrodes. Photographs and emission spectra of the DPJs, as well as bright regions in the DPJs, were obtained. Using the SPECAIR program, plasma parameters were calculated in different areas of diffuse plasma jets. It has been established that in the region where BALs appear, the average value of the electron temperature decreases.

The influence of Mg and Ca atoms on the optical breakdown threshold of a nonlinear ZnGeP₂ crystal at a wavelength of 2.097 mm is studied. An impurity was introduced using diffusion doping; the material was sputtered onto a ZnGeP₂ substrate, followed by annealing in vacuum at a temperature of 750 °C for 200 hours. It is shown that the introduction of Mg into a single crystal increases the optical breakdown threshold by 31%. When ZnGeP₂ is doped with Ca atoms, the opposite trend is observed. It is suggested that due to the creation of additional channels for energy dissipation of radiative and fast non-radiative relaxation processes through impurity energy levels, the optical breakdown threshold changes, which requires experimental confirmation.

In coastal water bodies formed by separation from the White Sea during the post-glacial uplift of the coast, in the chemocline (the gradient zone between the aerobic and hydrogen sulfide zones), a colored layer of water with a development of phototrophic microorganisms is often observed. The solar light transmission spectra measured at different horizons under water in three stratified water bodies in the coastal marine area using a submersible fiber optic probe are compared with the absorption spectra of light by water from the same horizons. In the layers with massive development of anoxygenic phototrophs, the concentrations of bacteriochlorophylls were determined from the absorption spectra. According to the data obtained, the ranges of the transmitted solar spectrum in the water column (“color ecological niches”) are largely determined by humic substances dissolved in water. Their concentration increases as the water body is isolated from the sea, due to which the photic zone narrows with depth, the chemocline becomes closer to the surface, and a shift towards longer wavelengths appears in the spectrum of light entering the chemocline. In the marine bay, the 520- 600 nm part of the spectrum reaches the chemocline, in the marine stratified lagoon, wavelengths of 510-6700 nm predominate, in reservoirs with a fresh surface layer of water, the solar spectrum is shifted to the red region (520-7200 nm). It is shown that "color ecological niches" in various water bodies are occupied by organisms whose light-collecting antennas are adapted to absorb light quanta of the corresponding spectral range.

Due to the importance of using the structure function for problems of optical radiation propagation in a turbulent atmosphere, the task of determining this function from the known mode coefficients of wavefront expansion was set. New formulas have been derived for the exact analytical calculation of the wavefront phase structure function on a circular aperture. Unlike the previously published analytical method, the proposed approach correctly accounts the entire domain, including the area near the edge of the aperture. The new method is compared to the published one and a numerical calculation with the distretization chosen sufficiently fine. The test samples comprised Kolmogorov wavefronts and Zernike polynomials and Karhunen-Loѐve functions corresponding to the Kolmogorov turbulence model. The deviations of the results of the published before method from the new one and from the numerical calculation are provided. The advantages and generality of the new method are stated and explained. The result will make it possible to accurately determine the structure function of the wavefront by its mode coefficients in problems of optical radiation propagation in randomly inhomogeneous media.

Micropowders made of transparent semiconductor and dielectric materials (ZnSe, MgF₂, CaF₂, SiO₂, BaF₂, MgAl₂O₄, Al₂O₃, Nd:Y₂O₃, YSZ, and TiO₂) are theoretically studied. The refractive indices of these materials are in the range 1.38 ¸ 2.48. As a result of calculations, it is found that the combination of scattering and interference of radiation increases its intensity by one or two orders of magnitude compared to the intensity of the incident radiation in a medium of particles several microns diameter. It is shown that this enhancement increases with the refractive index of the particle material. In our opinion, both nonlinear mechanisms of laser radiation absorption and avalanche ionization lead to an increase in the electron concentration in such local maxima. As a result, the material begins to heat up to the point of ablation.

The paper presents the results of numerical simulation of one of the least studied excimer lasers, a KrCl molecule laser. The simulation was carried out in a 1D approximation, where laser radiation were calculated along the optical axis between plane-parallel mirrors, and the system of kinetic equations and the Boltzmann equation were solved in each transverse layer of the active medium. The theoretical data well agree with the results for the EL series KrCl laser (HCEI SB RAS). The effect of the excitation discharge width on the energy characteristics of the laser is numerically shown. The suggested model and the obtained estimates can be used as tools for optimizing initial parameters when developing more powerful laser systems.

IR lasers are widely used in various fields of science and technology. In this regard, expanding the spectral range and obtaining effective generation in the IR is an urgent task. The object of our study is a laser based on the self-terminating transition of Eu atom with a radiation wavelength of 1.76 mm. In this work, we investigated the possibility of increasing the output parameters of such a laser by increasing the length of the active zone of the gas discharge tube (GDT). It is shown that increasing the volume of the discharge tube from 157 to 314 cm³ while maintaining the pump power level at 1200 W makes it possible to double the output power and laser efficiency. For the first time, an average radiation power of 2.5 W was achieved at the 1.76 mm line. The maximal efficiency of 0.3% is achieved at a pump power of 500 W. After 100 hours of operation, the energy characteristics of the Eu+Ne laser with an active zone volume of 314 cm³ demonstrated good repeatability, which allows us to conclude that it is possible to further increase the energy characteristics and lifetime of this laser. The results of the work can be used in microprocessing of materials, as well as in active optical systems associated with the visualization of fast processes.

The location of the electrodes of a copper vapor laser (CVL) discharge tube in cold buffer zones, where there are no metal vapors, leads to the formation of a phantom current before the “breakdown”. This necessitates the evaluation of whether the phantom current is an additional factor limiting the energy characteristics and what is the mechanism of this limitation? It is shown that at the initial stage of pumping, the intrinsic capacitance of the discharge tube is charged up to the “breakdown”, which determines two processes during this period of time - the population of metastable states of copper and the generation of a phantom current, which occurs as a result of shunting of the intrinsic capacitance of the discharge tube by the cold buffer zone from the anode side of the discharge tube. The mechanism of phantom current generation and its role in limiting the energy characteristics of CVL are considered. The studies indicate two problems on the way to improve the energy characteristics of CVL and the direction of search for their solution: the first is high pre-pulse concentration of electrons in the active medium and the second is the generation of a phantom current caused by processes in the cold buffer zones.