В работе исследована зависимость интенсивности линий Ca (393.3, 396.6, 422 нм), Fe (381.5, 382, 404.5, 406.3, 423.6 нм) от длительности лазерного импульса в методе филаментно-индуцированной эмиссионной спектроскопии. Филамент возбуждался в водном аэрозоле с распределением капель 0,8-2 мкм лазерными импульсами длительностью 65, 70, 230, 400, 500, 900 фс при неизменной энергии импульса - 3.0 мДж. Показано, что для с увеличением длительности лазерного импульса интенсивности эмиссионных линий исследуемых элементов возрастали.

Получены значения пределов обнаружения Al (396,15нм), Ba (553,35 нм), Ca (422,67 нм), Mg (285,21 нм), Na (588,99 нм) и Mn (403,08 нм) в жидко-капельном аэрозоле методом филаментно-индуцированной спектроскопии (R-FIBS) с использованием ультракоротких лазерных импульсов (60фс, 800 нм, 4,4 мДж). Получено значение предела обнаружения натрия по линии Na (588,99 нм) в жидко-капельном аэрозоле методом лазерной искровой спектроскопии (LIBS) с использованием лазерных импульсов короткой длительности (7 нс, 1064 нм, 550 мДж). Проведено сравнение полученных результатов в рамках используемых методов.

Background. Currently, the priority task is to develop the resources of the continental shelf. At the same time, ensuring the environmental safety of marine areas remains an important aspect. In this regard, the development and creation of robotic systems equipped with specialized complexes capable of solving a wide functional range of underwater operations is relevant. The purpose of this work is to create a hardware and software complex based on the method of laser-induced breakdown spectroscopy with the possibility of integrating it into a remotely operated underwater vehicle of the survey class for measuring the elemental composition of seawater and bottom rocks in the In Situ mode. Materials and methods. The analysis of the elemental composition of seawater and soil samples was carried out using the laser-induced breakdown spectroscopy method. A two-pulse diodepumped Nd: YAG laser DF-251 (SOL Instruments) was used as a source of laser plasma excitation. Results. An experimental hardware and software complex of an underwater spectrometer based on the method of laser-induced breakdown spectroscopy with the possibility of integrating it into existing remotely operated underwater vehicle (ROV) of the inspection class has been developed. Laboratory experiments were carried out to determine the chemical composition of a seawater sample. The possibility of using the presented hardware and software complex in the tasks of environmental monitoring of sea areas and geological exploration is shown. Conclusions. The obtained laboratory results make it possible to assert that the developed hardware and software complex is a promising solution for application in the problems of environmental monitoring of sea areas and geological exploration.

AbstractDynamics of the emission spectrum of a highly focused femtosecond laser pulse under filamentation in air have been investigated. A peak at 735 nm and a drop in the laser-beam intensity at the fundamental wavelength are observed in the spectrum of a laser pulse passed through the filamentation zone. It is shown that the peak is likely due to the Rabi splitting of the O I levels and breaking of the LS coupling for the 3 p ^5 P level in a strong laser field.

Экспериментально определены зависимости интенсивностей спектральных линий Ba I (413.24 и 553.55 nm) от времени задержки регистрации относительно лазерного импульса td в плазме оптического пробоя, генерируемого на поверхности водного раствора BaCl2 фемтосекундными импульсами (800 nm, 45 fs, 0.82 mJ). Максимальная интенсивность линии Ba I (413.24 nm) наблюдается при td=20 ns, в то время как интенсивность линии Ba I (553.55 nm), максимальна при td=40 ns. При td=10 ns интенсивность линии Ba I (413.24 nm) почти в 3 раза больше, чем для линии Ba I (553.55 nm), при вероятности спонтанного перехода для линии Ba I (413.24 nm) на два порядка ниже, что объясняется рекомбинационным каскадом. Для подсистемы уровней 5d6p 3Do и 6s6p 1Po не выполняется больцмановское распределение и отсутствует локальное термодинамическое равновесие. DOI: 10.21883/PJTF.2017.18.45038.16381

The results of experiments on the filamentation dynamics of high-power ultrashort Ti: sapphire laser pulses with wavelengths of 800 and 400 nm upon their sharp focusing in air are presented. The dependences of the position and dimensions of the plasma channel that forms in the region of the nonlinear beam focus on the laser pulse power are obtained. The spectra of the laser pulse during its filamentation are measured.

The possibilities of the combined use of laser spark spectroscopy (LSS) methods in the laser-induced fluorescence (LIF) of seawater are considered in order to study the carbon-containing matter and elements of the carbon cycle in seawater. During the analysis, the data on Sakhalin Island and the Amur estuaries were used. These regions were chosen in such a way that the dissolved organic matter in seawater was determined by either the living processes of the phytoplankton cells or other sources (terrigenous or anthropogenic). A linear bond between the carbon emission line in the LSS spectra of seawater and the intensity of the dissolved organic matter fluorescence in seawater was found in some regions when excited by green or violet radiation. It was shown that the common use of the LIF and LSS methods gives the possibility of finding some additional information on the content, nature, and type of the carbon-containing matter in seawater.

The investigational results on the dynamics of the spectra at laser break down at the sea water surface within a time interval of 0–30 µs are presented. The absorption lines of atomic hydrogen within 375–390 nm were recorded. To investigate the time dynamics of the intensity, the molecular bands of CN and OH were used, as well as the Na, Ca, and Mg resonance dublets; for the latter, the temporal dynamics of the ratio of line intensities to the background was studied. It has been shown that the time dependence of the ratio of line intensities (Na, Ca, Mg) to the background, the intensity of the continuous spectrum, and Na and Ca lines and molecular bands are approximated by the exponential dependence with two characteristic times, while the time dependence of the Ca line is approximated by the exponential dependence with one characteristic time.

Optical breakdown spectra on seawater and distilled water faces excited by Ti-sapphire laser pulses with durations of 50 fs and 650 fs were studied experimentally in normal atmosphere. The time dependence of the intensity of the Na I (588.9 nm) and Mg II (279.5 nm) emission lines was studied, and the limit of detection of Na in an aqueous NaCl solution was established at 10−6 g/l.

The collision of plasma fronts upon laser breakdown in atmosphere under normal conditions has been studied. This interaction leads to an increase in the integral luminosity (which can be 85% higher than that for the noninteracting plasmas, depending on the regime of motion of the colliding plasma fronts) and in the intensity of emission lines on the background of continuous emission from laser plasma.

The plasma front propagation regimes and the spectral characteristics of plasma emission upon laser breakdown in the normal atmosphere are experimentally investigated. The molecular emission of atmospheric gases is recorded at the initial instants of the development of the laser plasma. The behaviour of the intensities of continuous and line emission spectra is investigated upon interaction of counterpropagating plasma fronts; in this case, an increase in the integrated intensity of the plasma emission and a rise in the contrast of emission lines against the background of continuous plasma emission was recorded.

The results of investigation of the dynamics of the emission spectra of a plasma generated at the surface of liquid and solid targets by a laser pulse of a complex time form are presented. It is shown that the shock wave arising as a result of breakdown on the surface of the solid and developing to heights of the order of 4 mm is a laser-supported detonation shock wave. In the case of solid targets, we recorded additional laser plasma light pulses coming after the main pulse. Two additional light pulses have been recorded for the emission line AlI 396.1 nm. In the case of the liquid, we have not detected additional pulses for the investigated emission lines of the elements at the laser radiation power densities used.

Experimental studies of the laser-induced Al plasma expansion during laser pulse into ambient air under pressures of 76 - 760 Torr was performed using 2-channel ADC attached to photomultipliers. Simultaneous measurements of the temporal dynamics of entire plasma emission and neutral Al 396.15 nm emission vs. laser pulse form were carried out with resolution 10 ns. It was detected dualization of a plasma head front, corresponding laser Q-switched pulse. This phenomena may be caused by decay of the laser-supported detonation wave. Distance on which plasma front observed vs. time was obtained under different pump energy of Nd:YAG laser. These results show that plasma expansion dynamics can be described by fast ionization wave model and laser- supported detonation wave model depending on laser pulse form.

The results of experimental estimation of the fulfillment of the local thermodynamic equilibrium (LTE) criterion for the plasma generated by laser pulses of various duration at the surface of a solid target placed in a gaseous atmosphere at standard pressure are given in the present paper. The fulfillment of all the LTE criteria is demonstrated for an ensemble of neutral atoms contained in the plasma generated by a giant laser pulse or by a laser pulse whose complex shape represents several giant pulses against the background of free-running laser oscillations. The plasma excited by the radiation of a Nd : YAG laser with energy ≤ 0.4 J per pulse is examined. We have recorded a resonance broadening of atomic Al and Mg lines. This has allowed us to estimate the density of neutral atoms contained in a plasma plume.

This article reports the results of an experimental investigation of the basic mechanisms that cause the broadening of emission lines of a laser-induced plasma generated on the surface of rigid targets in a gaseous atmosphere. The contribution of Stark and resonance mechanisms of emission-line broadening for the resonance doublet Al I 3s 2 3p 2 P 3/2,1/2 -3s 2 4s 2 S 1/2 and triplet Mg I 3s3p 3 P 0,1,2 0 -3s4s 3 S 1 is discussed. The concentrations of neutral Al atoms in the laser-induced plasma are evaluated by the magnitude of resonance line broadening.

The intensities, widths, and shifts of the centres of the emission lines of a laser plasma generated on the surfaces of solid targets were determined experimentally as a function of the ambient gas pressure, The Stark broadening and the Stark shift of the emission lines were used to estimate the electron temperature and the electron density at various gas pressures.