Atmospheric and Oceanic Optics最新文献

The results of aerosol condensation activity obtained at the Siberian ZOTTO background station (60.8° N, 89.35° E) are presented. The measurements were carried out during the growing season from June 18 to July 6, 2021. The condensation activity of aerosol particles was estimated from cloud activation spectra measured depending on the supersaturation of water vapor and the aerosol particles size. Based on these data, the size distributions of activated particles, the critical diameters of cloud activation, and the hygroscopicity parameter of aerosol particles are calculated. The obtained cloud activation parameters are compared with similar data obtained at background stations in the Amazon rainforest and boreal forests of Northern Europe.

Evaporation is a fundamental process in the hydrological cycle. Accurate prediction of evaporation is essential for effective water resource management, flood forecasting, and the development of adaptive strategies to mitigate the impacts of climate change. This work analyzes the capabilities of Seasonal Autoregressive Integrated Moving Average (SARIMA), Random Forest, and Support Vector Machine machine learning models in predicting evaporation in the south-western part of Nigeria. The results show that the SARIMA performs best in Ikeja, Akure, Ado Ekiti, Ibadan, and Osogbo. Its highest score (R²) was observed in Ibadan (0.9859) followed by Akure (0.9159), Ado Ekiti (0.8711), and Osogbo (0.8509). This suggests that 85% to 98% of the variability in evaporation in these locations can be explained by the meteorological inputs, which is good given the complexity and non-linearity of the atmospheric process. Moreover, we revealed a decreasing regional trend from 2001 to 2010, which suggests a decline in solar radiation and/or air temperature.

The study of the spatial orientation of ice crystals in cirrus clouds is a relevant problem in atmospheric optics, as the orientation of particles significantly influences the process of solar energy transfer in the atmosphere. The systematic carrying out of such observations is challenging due to the lack of available instruments. This article presents a new type of lidar – a two-beam polarization lidar – that enables the necessary observations. The numerical simulations of the signal from this lidar as a function of the sounding beam angle are described. The obtained numerical solution has been verified using experimental data collected with a scanning polarization lidar.

One approach to constructing terahertz radiation sources for analyzing atmospheric gas composition is based on the use of nonlinear optical generators that convert the frequencies of intense near-infrared laser sources. This method’s downside is that its efficiency is proportional to the square of the generated frequency. This paper proposes a solution based on the use of cascade conversion, which involves generating intermediate frequencies in a local infrared transparency window of a nonlinear crystal and then downconverting these frequencies to the subterahertz region. For the first stage, an enhanced conversion due to a significant increase in quadratic susceptibility near optical phonons or stimulated polariton scattering is allowed. A second-stage model is considered for the process of subterahertz difference frequency generation under pumping in the local infrared transparency window in a KTP crystal. The fulfillment of collinear phase matching is demonstrated, and the figure of merit is estimated.

The paper theoretically and experimentally studies the kinetics of decay of radiation on the laser transition of Yb³⁺ ion in the matrix of ceramic samples made of yttrium oxide. nanopowder doped with Yb and Zr. The calculation results showed the presence of a source of pumping of the upper level of Yb³⁺, presumably in the form of defects with a nearby lower energy level, in the ceramic samples, which explains the longer “tail” of the oscillograms than follows from a purely exponential decay. During pumping, the levels of these defects are saturated with energy, and after the pumping ceases, they give it to ytterbium ion, transferring it to the upper level of Yb³⁺. The energy exchange is quite weak and, most likely, have an insignificant effect on the energy of laser radiation of the samples. We also study the influence of the well-known “radiation trapping” effect on photoluminescence decay time in samples of different thickness. The saturation effect of the increase in photoluminescence decay time has been experimentally detected depending on the thickness. For a sample of 5% Yb:Y₂O₃ with addition of ZrO₂, this thickness was 1180 microns. To explain this effect, a mathematical model was developed based on the numerical solution of Biberman–Holstein integro-differential equation. The agreement between the calculated and experimental data confirms the correctness of our view of the physical processes in ceramic samples.

The detection limits for a series of elements (Na, Ca, Ba, and Al) in a water aerosol were determined to be tens of micrograms per cubic meter for Al, and in the range of single micrograms per cubic meter for Na, Ca, and Ba. The possibility of using the laser-induced breakdown spectroscopy method as part of compact mobile systems for monitoring atmospheric aerosol is demonstrated. The dependence of the detection limits of the specified elements on the energy of exciting laser pulse, as well as on the numerical aperture of a beam is investigated. The existence of optimal focusing conditions is shown.

This paper explores the propagation characteristics of perfect vortex beams (PVBs) in atmospheric turbulence and evaluates their performance as optical communication links. The aperture averaged scintillation index of PVBs under turbulent conditions is calculated, along with the mean signal-to-noise ratio (SNR) and mean bit error rate (BER) when employed as optical links. The influence of various PVB parameters on the aperture averaged scintillation index, mean SNR, and mean BER is systematically analyzed. The findings of this study are expected to aid in the advancement of optical systems operating in atmospheric turbulence conditions.

The energy and spectral characteristics of radiation generated using the first type of phase matching in the wavelength range 3.3–6.57 μm by a ZnGeP₂ single-crystal optical parametric oscillator pumped by a Ho:YAG laser were studied. The experimentally attained maximal average OPO radiation power was ∼4.63 W at the signal wave at a pulse repetition rate of 10 kHz with a generation efficiency of 44.67% and ∼680 mW at the idler wave at a pulse repetition rate of 10 kHz with an efficiency of ∼6.57%. The developed OPO is promising for medical applications in the field of non-invasive surgery for dual-wave action on human organic tissue for the purpose of tissue ablation.

Nonlinear propagation of high-power femtosecond laser pulses in the filamentation regime in air at different pressures is theoretically studied. Due to scaling laws which relate the density (pressure)of the propagation medium to the initial laser pulse parameters, our study allows for predicting the formation of a nonlinear focus during self-focusing and the formation of a filamentation region on real atmospheric paths hundreds of meters long. The results make it possible to better understand the complex and multifactorial dynamics of the filamentation of powerful ultrashort laser radiation and open up new prospects for optimizing and expanding the range of applications based on this phenomenon, in particular, for remote diagnostics of atmospheric components and energy delivery along long distances. Numerical simulation is carried out on the basis of the reduced (time-integrated) nonlinear Schrodinger equation for the optical field envelope, which governs the nonlinear propagation of high-power femtosecond pulses of a titanium-sapphire laser under conditions of a 16-fold change in air pressure. The formation of the multifocal optical structure in the filamentation region, which is especially evident in these conditions, is considered in detail.

The appearance, size, and density of micro ice crystal particles play a crucial role in weather forecasting and modification. Current observation methods are predominantly offline, requiring sample transfer from cloud chambers to microscopes for analysis, which lacks real-time capability and continuous monitoring. To address this, we designed and constructed an in-situ microscopic observation system for real-time monitoring of ice crystal formation and growth. This system successfully captured dynamic morphological changes and size distributions of ice crystals under both natural and catalyzed conditions. Using bismuth iodide (BiI₃) and silver iodide (AgI) as catalysts, it is observed that AgI significantly enhances ice nucleation efficiency, reducing the average ice crystal size to 30 μm and increasing the number density to 1 × 10⁷ ice crystals/m² at −16°C. BiI₃ showed a weaker catalytic effect. The system demonstrates high potential for applications in artificial precipitation, hail suppression, and climate research.