Atmospheric and Oceanic Optics最新文献

Sources of short-wavelength radiation generated by the interaction of high-intensity radiation with matter are in demand for experimental research in physics, chemistry, and biology. Reproducible parameters of the generated short-wavelength pulses require the use of femtosecond pulses with stabilized carrier-envelope phase (CEP). The work is devoted to the study of the effect of pulse envelope noise on the error in determining the CEP. For the CEP stabilization system based on f-2f interferometer with spectral interference pattern resolution, it is shown that an increase in noise of an original pulse increases the error in determining CEP from supercontinuum radiation, which attains about 100 mrad at an envelope noise of 1%. An increase in the radiation peak power increases the influence of noise on the error in determining CEP due to supercontinuum generation. The results can be used to develop and optimize systems for measuring the carrier-envelope phase of femtosecond pulses with repetition rates in kilohertz range.

One of the fundamental directions in the development of lasers based on self-terminating transitions (RM transitions) in metal atoms and ions is their use in brightness amplification systems. Improvement of these systems requires expanding the operational spectral range and increasing the pulse repetition frequency. A promising approach to addressing these challenges is the use of a new class of high-speed high-frequency switches based on a slit discharge (eptrons) for pumping RM lasers, particularly those operating in the UV range. Within this approach, this paper studies the frequency-energy characteristics of a mercury ion RM laser (λ = 398.4 nm). The use of a high-speed slit-discharge switch enables generating voltage pulses with a rise time of 2–3 ns across the electrodes of a gas-discharge tube and lasing in a double-pulse mode at repetition frequencies up to 300 kHz. It is ascertained that the laser pulse energy strongly depends on temperature and pulse repetition frequency, and the optimal frequency decreases as the temperature increases. Lasing in the form of bursts of four pulses has been demonstrated. The achieved high pulse repetition frequencies of the laser radiation at the short wavelength can contribute to the creation of unique brightness amplifiers based on an Hg⁺ RM laser.

Natural water contains dissolved organic matter (DOM) which plays an important role in biogeochemical processes and affects the functioning of aquatic ecosystems. The paper analyzes the spectral and luminescent characteristics (optical indices, difference absorption spectra, fluorescence quantum yield, and protein-like fluorescence) of DOM chromophoric fraction (CDOM) in two meromictic reservoirs on the coast of the Kandalaksha Bay of the White Sea (the Elovoe and Trekhtzvetnoe lakes) based on the results of expeditionary work in 2025. The difference in optical indices in different layers of the reservoirs (the surface fresh layer, the intermediate brackish aerobic layer, the chemocline, and the saline bottom hydrogen sulfide zone) and their relationship with hydrochemical parameters are shown. An increase in the quantum yield of CDOM fluorescence in the chemocline of the Lake Elovoe and its decrease in the Lake Trekhtzvetnoe are explained. The results are of importance for ecological monitoring of aquatic ecosystems, as well as for understanding the processes that affect optical CDOM characteristics of natural water.

This work continues the study of a possibility of using laser fragmentation/laser-induced fluorescence (LF/LIF) for the remote detection of nitrocompounds (NC) and organophosphorus compounds (OPC). A technique for simultaneous detection of surface traces of NС and OPС is discussed. It is experimentally shown that exciting laser radiation at a wavelength of 246.824 nm, which falls in the region of overlapping rotational lines of γ(0, 2) and γ(0, 0) bands of NO and PO absorption spectra, can be used for simultaneous excitation of fluorescence of NС and OPС photofragments. To improve the noise immunity of the LF/LIF detection technique, it is suggest to use sounding laser radiation wavelength from the range of overlapping γ(0, 2) and γ(1, 1) bands of the absorption spectra of NO and PO fragments in excited vibrational states after fragmentation. The resulting intense anti-Stokes γ(0, 1) and γ(1, 0) fluorescence bands are located in the spectral range 235–240 nm and do not overlap with the spectra of broadband Stokes fluorescence of surface materials bearing traces of NС and OPСs. The results can be used in the development of a universal system for the simultaneous detection of surface traces of explosives and toxic substances by LF/LIF method.

Plant protection measures against various pathogens must be implemented in a specific period of time to avoid potential economic losses. Objective and reliable automated plant health diagnostics requires new approaches and their integration into traditional monitoring and assessment systems. This paper describes an experimental setup which detects high levels of plant stress hormones in air due to mechanical damage from direct atmospheric radiation absorption based on Fourier transform infrared spectroscopy. The results of this study, on the one hand, open a possibility of detecting plant stress by analyzing the atmospheric absorption spectrum above a plantation, and on the other hand, identify a wide range of fundamental problems, the solution of which will promote the development of an effective method for remote diagnostics of plant health.

A gas discharge is an effective converter of electrical energy into optical radiation. The mechanisms of current development and the quantitative contribution of electron multiplication and emission processes remain undetermined, even in the simplest discharge types, such as the abnormal glow discharge. In this work, the current–voltage characteristics and the voltage distribution in the cathode sheath region of a DC discharge in helium are investigated in the pressure range of 3.5–9 torr and the voltage range of 200–1700 V. The nonmonotonic behavior of the current–voltage characteristics is demonstrated under conditions minimizing controlled and uncontrolled impurities. It is shown that if the powers deposited into the discharge exceed 3.5 W, a deviation from the asymptotic approximation of the cathode fall length of the potential to a value of 0.37 of the normal length is observed, which is associated with a change in particle concentration in the cathode region. The derived empirical law made it possible to refine known approximations for the dependence of temperature and particle concentration on the power deposited into the discharge, which is relevant for describing the kinetics of processes in high-voltage gas discharges used as sources of optical radiation.

Studying the spatial distribution and temporal variation in the concentration of greenhouse gas methane (CH₄) in the Arctic is a relevant but difficult scientific problem. Reanalysis data can serve an additional source of information, but they require regular validation. This work estimates the reproducibility of surface CH₄ concentration in the Arctic region by CAMS global greenhouse gas reanalysis database version EGG4. Reanalysis data on the variations in surface CH₄ concentrations are compared with continuous measurements at the research station “Cape Baranov Ice Base” (79°16′ N, 101°45′ E) in 2016–2020 on different time scales (interannual, seasonal, and daily). It is found that the reanalysis data reflect the interannual variability of surface CH₄ concentrations the worst. The seasonal variability of the CH₄ concentration is well described by the reanalysis data; the model amplitudes of the seasonal cycle are slightly higher than the actual ones. The model and actual values of surface temperature and wind speed and direction are also compared. This verification of the CAMS database is useful before its use in regional-scale numerical simulation and other applied problems.

Hard ionized (e.g. electron-beam excitation, pre-ionized discharge) high pressure (>0.5 bar) neon emits a distinct ultraviolet continuum in the 200–450 nm spectral range, which has not yet been unequivocally attributed to any particular neon transition. The intensity of this continuum scales with squared neon pressure, and thus can directly be linked to a molecular neon precursor. Concurrently, hydrogen line emission, particularly a very strong Lyman-α (121.57 nm), as well as Hα (656.3 nm) and Hβ (486.1 nm) lines can be observed. This work shows that no hydrogen line emission and, particularly, no UV-continuum emission can be observed in highly purified hydrogen-free neon. Only after deliberately adding small amounts of hydrogen into the buffer gas neon, the hydrogen lines, and particularly the UV continuum, are being emitted. Furthermore, the intensity dependence of all structures on hydrogen partial pressure essentially coincide and show a distinct maximum at about 0.7 Pa, largely independent of the absolute neon base-pressure. The UV continuum thus clearly originates from excited hydrogen species, and is attributed here to the ({{a}^{3}}Sigma _{g}^{ + } to {{b}^{3}}Sigma _{u}^{ + }) hydrogen excimer transition. Excitation of the upper ({{a}^{3}}Sigma _{g}^{ + }) level is proposed as energy transfer from neutral neon excimer molecules: while part of the ({text{Ne}}_{2}^{*}) energy is sufficient to dissociate and excite hydrogen molecules into an H + H (n = 2) configuration, leading to successive Lyman-α radiation, Ne₂ excimer molecules close to the so called “classical left turning point” lack the necessary energy, but can readily excite hydrogen molecules directly from the ({{X}^{1}}Sigma _{g}^{ + }) ground state into the ({{a}^{3}}Sigma _{g}^{ + }) bound molecular state.

Harmful algal blooms pose a serious threat to the ecology of coastal waters. Their timely detection is a crucial task in environmental monitoring. Optical spectrofluorimetry can be a promising approach in this field. The subject of this scientific work is the study of normalized fluorescence temperature curves (NFTC) as reference features of hazardous microalgae and confirmation of the possibility of identifying the genera of hazardous microalgae under study with their help. NFTC were obtained in laboratory experiments with microalgae monocultures under controlled conditions with registration of fluorescence spectra during linear heating (20–80°C). Verification was carried out by means of cluster analysis using the principal component analysis (PCA). The study has shown that NFTC demonstrate stable genus-specific patterns, making it possible to distinguish microalgae at the genus level with an accuracy of 90.91%. The use of PCA (three principal components which explain 94.22% of the variance) eliminates clustering errors caused by multicollinearity of the original features. The highest classification accuracy is achieved for Heterosigma akashiwa (100%), and the lowest, for Pseudo-nitzschia (86.15%) due to intrageneric similarity of NFTC. The study shows the need to expand the catalog of standards to enhance the statistical significance of the results.

The development of laser radiation sources in the yellow-red spectral region with an extended range of adjustable generation parameters is a relevant and sought-after task in biomedical applications. This work experimentally studies spectral, temporal, spatial, and energy characteristics of Ne atom radiation excited by a pulsed inductive cylindrical discharge. Lasing was obtained at 3p → 3s transitions of neutral Ne atoms at wavelengths of 594.4 and 614.3 nm. The intensity ratio of these spectral components I₅₉₄ : I₆₁₄ depended on the pumping conditions and varied from 1 : 1 at pressures of 0.2–0.3 torr to 1 : (2…4) at an optimal pressure of about 0.13 torr. A maximal lasing energy of 17 μJ was achieved at a charging voltage of 29 kV (limited by the excitation system characteristics). A decrease in charging voltage below 20 kV resulted in the breakdown of lasing. The study of the temporal lasing characteristics revealed that lasing at the both wavelengths began simultaneously. The pulse duration was identical and attained an average of 12.5 ± 0.5 ns (FWHM), which corresponded to a pulse power of over 1.4 kW. These results can be used to develop gas-discharge lasers with tunable radiation parameters for ophthalmic applications.