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Two techniques for multielement analysis of liquid-droplet aerosol are compared, which are based on the spectral analysis of the radiation of a laser plasma generated in a laser breakdown (LIBS) or during laser pulse filamentation in a liquid droplet aerosol (R-FIBS). A liquid-droplet aerosol containing Na solution is used. It is shown that there are optimal delay times of the start of signal recording relative to the start of plasma generation, at which the signal-to-noise ratio is maximal, for both techniques. The dependence of the signal-to-noise ratio is derived for different laser radiation focusing deep into a liquid-droplet cloud for LIBS. The Na detection limits are determined for both methods.

The capabilities of filament-induced breakdown spectroscopy for the analysis of the elemental composition of aqueous aerosols were estimated. The diameter of aqueous aerosol droplets in the atmosphere was 0.8–2.0 μm. The emission lines of the chemical elements were excited by fi lamentation of femtosecond laser pulses (60 fs, 800 nm, 4.4 mJ) in weak focusing mode by a lens with a focal length of 500 mm. The obtained limits of detection for Al (396.15 nm), Ba (553.35 nm), Ca (422.67 nm), Mg (285.21 nm), Na (588.99 nm), and Mn (403.08 nm) in an aqueous aerosol were 12.1, 41.7, 10.0, 7.3, 0.7, and 32.3 mg/L, respectively.

The temporal evolution of the width and shift of N I 746.8 and O I 777.4 nm lines is investigated in a filament plasma produced by a tightly focused femtosecond laser pulse (0.9 mJ, 48 fs). The nitrogen line shift and width are determined by the joint action of electron impact shift and the far-off resonance AC Stark effect. The intensive (I = 1.2·1010 W/cm2) electric field of ASE (amplified spontaneous emission) and post-pulses result in a possible LS coupling break for the O I 3p 5P level and the generation of Rabi sidebands. The blueshifted main femtosecond pulse and Rabi sideband cause the stimulated emission of the N2 1+ system. The maximal widths of emission lines are approximately 6.7 times larger than the calculated Stark widths.

The results of experiments on the study of spatial characteristics of the multiple filamentation domain of GW Ti:Sapphire laser pulses in glass are presented. The dependences of the coordinates of the beginning, end, and diameter of the multiple filamentation domain (MFD) vs the laser pulse energy are derived. It is found that when the average intensity in the beam attains certain values, MFD is formed near the illuminated side of the glass sample. When the beam intensity attains a threshold, the secondary MFD is formed; its spatial characteristics depend on the pulse-periodic irradiation exposure time. The diameter of the secondary MFD and coordinates of its beginning depend on the exposure time. The spatial characteristics of the primary MFD were independent of the exposure time during the experiments.

Results of an experimental study of spatial parameters of the region of multiple filamentation of gigaand terawatt pulses of a Ti:Sapphire laser in glass and water are described. The pulse-power dependencies of the coordinates of the filamentation region, the number of filaments, their distribution along the laser beam axis, and the mean length of the filaments are presented. It is shown that the spatial parameters of the filamentation region are qualitatively similar in water and glass. It is found that the number of filaments along the region of multiple filamentation is a unimodal distribution. When increasing the radiation power, the length of individual filaments in the region of multiple filamentation is reduced, and their diameters are quasi-constant at all power values implemented in the experiment. When attaining a certain power of laser pulses with a Gaussian energy-density distribution, the filamentation region takes the shape of a hollow cone with the apex directed to the radiation source.

The regularities of multiple filamentation of gigawatt femtosecond laser pulses in a solid dielectric (optical glass) have been considered. The fine spatial structure of the plasma region that is formed under glass photoionisation and accompanies the formation of light filaments is analysed experimentally and by means of numerical simulation. The dependence of the number, position, and extension of individual 'generations' of plasma channels on the laser pulse energy has been investigated for the first time. It is found that the distribution of the number of plasma channels over the length of a dielectric sample has a maximum, the position of which correlates well with the position of the nonlinear focus of the light beam as a whole; at the same time, the average channel length decreases with increasing pulse power, whereas the number of successive channel 'generations', on the contrary, increases.

The influence of the energy of femtosecond laser pulses on the intensity of Fe I (371.99 nm) emission line and the continuous spectrum of the plasma generated on the surface of Fe3+ water solution by a Ti: sapphire laser radiation with pulse duration < 45 fs and energies up to 7 mJ is determined. A calibration curve was obtained for Fe3+ concentration range from 0.5 g/L to the limit of detection in water solution, and its saturation was detected for concentrations above 0.25 g/L, which is ascribed to self-absorption. The 3σ- limit of detection obtained for Fe in water solution is 2.6 mg/L in the case of 7 mJ laser pulse energy. It is found that an increase of laser pulse energy insignificantly affects on LOD in the time-resolved LIBS and leads to a slight improvement of the limit of detection.

The digital images of plasmas induced by tightly focused Ti:Sapphire laser (1.1 mJ, 48 fs) in air reveal new fluorescent structures not observed for slightly focused beams earlier. The fluorescent structures arise because of lens aberrations. The energy absorbed by femtosecond laser plasma has nonlinear dependence on incident laser energy. The threshold peak power for filament formation is 5.2 GW. Time-resolved spectroscopy of plasmas shows short-time emission of molecular bands (up to 1 ns) and long-time emission of atomic lines (up to 150 ns). Initially, second positive system of N 2 and first negative system of N 2 + are observed. The atomic lines are formed with delay of 50-80 ps relative to molecular ones. Lines of N 2 and N 2 + demonstrate different temporal behavior, while lines of N I and O I have the same intensity time dependence. Peak intensities of second positive system of N 2 and first negative system of N 2 + are separated by 50 ps time interval.

We present the results of sensing of the atmosphere in the condition of a transition 'continent - ocean' zone by means of giga- watt femtosecond pulses of the fundamental and second harmonics of a Ti : sapphire laser. In the regime of multi-frequency sensing (supercontinuum from the fundamental harmonic) the emission lines of the first positive system of the nitrogen molecule B 3 Pg - A 3 Su have been recorded, while the sensing using of the second harmonic have revealed the possibility of detecting the lines of Raman scat- tering of nitrogen ( l = 441 nm). The intensity ratio of the line of Raman scattering of nitrogen and the line of elastic scattering at the wavelength of l = 400 nm amounts to 5.6 ´ 10 -4 .

The influence of pulse repetition rate of a femtosecond Ti:Sa laser (800 nm, 45 fs, 0.82 mJ) on intensity of spectral lines at optical breakdown on the surface of CaCl2 water solution is experimentally determined. It is demonstrated that, with increasing pulse repetition rate from 20 to 1000 Hz, the intensity of Ca II (393.3 nm) emission line reduces by 44%, while the plasma continuum remains unchanged within measurement error.

Our work is dedicated for review of the synthesis of the new nanocomposite media with Au and CdS nanoparticles. Also formation of filament structure in presented samples as result of interaction with femtosecond laser pulses in depending on the component composition of the samples and the various experimental conditions was investigated.

The composition of the line and band spectra of the plasma induced by a femtosecond laser pulse on the surface of sea water is determined. The temporal behaviors of the intensity of the continuum and the Ca II, Mg II and Na I lines are investigated. It is shown that the time dependence of the intensity of the Na I line is described by a monoexponential function. The characteristic decay times of the line intensities of Mg II and Na I were used to estimate the three-body recombination times. Using these values, we estimate the electron number density and the feasibility of Local Thermodynamic Equilibrium (LTE) criterion. A method involving excitation rate constants is proposed for the comparison of detection limits. For a plasma generated on a liquid surface, the following relation among detection limits will be obtained: LOD(Na)

The possibility of using hybrid silicate nanocomposite materials on the basis of polysaccharides and hyperbranched polyglycidols for efficient conversion of pulsed radiation of a femtosecond Ti : sapphire laser at the wavelength 800 nm into supercontinuum in the range from 400 to 1000 nm is experimentally demonstrated. It is established that the addition of a small concentration of Au and CdS nanoparticles to the studied materials essentially affects the efficiency of conversion of the laser radiation energy into the supercontinuum spectrum.

The transmission of the femtosecond laser pulses by new biosilicate nanocomposite materials has been experimentally investigated. The strong nonlinear optical properties of these nanocomposite structures have been revealed in spectral characteristics of transmitted ultrashort pulses. The shape of transmitted spectrums through new nanocomposite biomaterials demonstrates major changes indicating the broadening with formation a strong anti Stokes component in the output spectrum with generation of supercontinuum spectra. The carried out studies have showed that the optical nonlinearity of new nanocomposite materials can be regulated by trace amounts of Au or CdS nanoparticles.

Characteristic decay times of continuum and emission doublet intensities (MgII 279.6 and 280.3, CaII 393.4 and 396.8, NaI 589 and 589.6 nm) are presented. Measurements were carried out for plasma induced by a 42-fs laser pulse within a time interval of 0–85 ns. It is shown that the NaI doublet intensity is described by a monoexponential dependence throughout the whole observation time interval. Using the triple recombination coefficient, the electron density has been estimated to vary from 3.0 × 1016 to 2.4 × 1015 cm−3. The validity of the local thermodynamic equilibrium criterion and the dependence of the line intensity-to-background ratio on the delay time are studied.

We have evaluated the feasibility of using femtosecond laser-induced breakdown spectroscopy with time-resolved detection of the spectra for determination of trace concentrations of chemical elements in water. The laser plasma was generated on the surface of aqueous solutions by a single pulse from a titanium:sapphire laser (pulse duration 40 fs, pulse repetition frequency up to 1 kHz). We obtained the 3σ limits of detection (LODs) for Al, Ba, Ca, Cu, Fe, K, Mg, Na, Zn in water as 0.19, 0.08, 0.01, 0.78, 3.4, 0.006, 1, 0.0009, 2.5 mg/L respectively.

The spectral and temporal characteristics of plasmas produced by femtosecond laser pulses acting on seawater surfaces are studied. The time dependence of the decay in the intensities of emission lines and the continuum are determined and the electron density is estimated using the three-body recombination time. It is shown that an atomic line with a low excitation potential is the most sensitive for femtosecond laser induced breakdown spectroscopy.

The transmission of laser femtosecond pulses by spicules of marine glass sponges and monolithic amorphous nanocomposite silica biomaterials synthesized on the basis of natural polysaccharides has been experimentally investigated. The strong non-linear optical properties of these biominerals have been revealed in spectral characteristics of transmitted ultra-short pulses (USP). Comparative analysis of the transmission spectra of USP reveals that spicules exhibit much stronger non-linear optical properties than quartz optical fibers. Recently new monolithic nanocomposite silica biomaterials were synthesized on the basis of various natural polysaccharides and completely water-soluble Si-precursor. The shape of transmitted spectrums through both spicules and new nanocomposite biomaterials demonstrates major changes indicating the broadening with formation markedly strong anti-Stokes component in the output spectrum with generation of supercontinuum spectra. The carried out studies have showed that the nature combination of spongin protein with silicon dioxide extracted from seawater by silicatein protein in glass sponge spicules and monolithic nanocomposite silica biomaterials are biological and biomimetical nanocomposite materials with unique optical properties.

Spectral and time characteristics of a hydrogen HI 656 nm emission line are experimentally investigated during optical breakdown generated by pulses of the first harmonics of a femtosecond Ti:Sapphire laser on the water surface. The electron density of the generated plasma is estimated.

The fraction of focused femtosecond laser radiation energy absorbed by a laser-induced spark in air has been studied. It is established that the absorbed energy exhibits nonlinear growth with increasing energy of the laser pulse. The threshold power for laser-induced spark formation in air is 5.2 GW.

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.

We present the results of measurement of the laser-induced fluorescence spectra of sea water under laboratory conditions. We show that during phytoplankton cell death caused by heating of sea water samples, the fluorescence intensity of dissolved organic matter (DOM) increases. We observe different behaviors of the fluorescence intensity for excitation by 2nd harmonic (532 nm) and 3rd harmonic (355 nm) emission from a Nd:YAG laser during degradation of dissolved organic matter. In the first case, a monotonic decrease in the DOM532 fluorescence intensity occurs, while in the second case the fluorescence intensity remains constant. We give a possible explanation for such behavior of the DOM fluorescence intensity.

The influence of the diameter of the beam of a femtosecond Ti:Sapphire laser (800 nm, 40 fs, 0.8 mJ) on the intensity of spectral lines upon optical breakdown on the surface of CaCl2 aqueous solution has been determined experimentally. It is shown that an increase in the laser-beam diameter from 7 to 14 mm on a focusing lens for identical pulse energy increases the intensities of the CaII (393.3 nm) and Hα (656 nm) lines by factors of 3 and 20, respectively. This effect can be used to increase the intensities of emission lines of chemical elements in femtosecond laser-induced breakdown spectroscopy of liquids and, accordingly, improve the sensitivity of this method.

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.

A comparison technique is proposed for detection limits of elements using the rate constants of excitation from the ground state. It is shown that the limits of detection (LOD) will be in the relation: LOD(Na) < LOD(Ca) < LOD(Mg).

We have studied the efficiency of fluorescence excitation in chlorophyll a by the second harmonic (532 nm) and the third harmonic (355 nm) of an Nd:YAG laser for sea water samples with phytoplankton taken during different algal blooms and for extracts of higher plants diluted with sea water. We have shown that when using the second harmonic, the efficiency of fluorescence excitation in chlorophyll a is more than twice as high as for excitation by the third harmonic. We discuss the advisability of using the second or third harmonics of the emission from an Nd:YAG laser when studying the biooptical parameters of sea water.

Time-resolved spatial and spectral characteristics of laser plasmas interaction in normal atmosphere are presented. Plasma experiments were performed by using 532 nm (4 ns, 180 mJ) and 1064 nm (5 ns, 360 mJ) pulses from Brilliant B Nd:YAG laser. Laser beams were focused in the opposite directions by lenses with focal distances of 15 mm. Firstly laser breakdown of air by 532 and 1064 nm laser radiation was investigated. Molecular bands, absorption line of atomic oxygen O 777 nm and dip of continuum intensity are recorded at initial instants of laser plasma formation. Mechanisms of plasma expansion are investigated. Relationship of molecular bands, absorption line of atomic oxygen, plasma's UV radiation and fast wave of ionization is discussed. Molecular bands, continuum and line temporal dynamics was investigated during laser plasmas interaction. Three zones of interaction and enhancement of line/continuum ratio is registered. Influence of KrF laser radiation (248 nm, 25 ns, 600 mJ) on parameters of breakdown induced by 532 nm laser radiation is discussed.

Dynamics of the chlorophyll "A" and dissolved organic matter fluorescence induced by laser radiation at 355 and 532 nm was analyzed. Formation of the seawater laser induced fluorescence spectra was investigated during photosynthesis cells destruction and dissolved organic matter (DOM) degradation processes. Experiments were carried out in laboratory conditions. It was showed that decreasing of the intensity of the chlorophyll "A" fluorescence connected with increasing of the dissolved organic matter fluorescence. Fluorescence spectra dynamics is differ for 355 and 532 nm laser radiation wavelengths.

Laser plasmas interaction and spectral characteristics of plasma were investigated at a laser breakdown in a normal atmosphere with the purpose of improving laser-induced breakdown spectroscopy sensitivity. Colliding plasmas interaction was investigated depending on mechanism of absorption wave of laser radiation and distance between foci. Laser supported detonation wave, breakdown wave and fast wave of ionization are absorption wave observed in experiment. It was shown that seed electrons for cascade breakdown in front of fast wave of ionization is occurred due to oxygen molecules photoionization. Molecular emission and collapse of intensity of plasma continuum during the initial moments of laser plasma expansion were registered. The line/continuum ratio was essentially increased in case of laser plasmas interaction. Thus laser plasmas interaction improves sensitivity of LIBS.

The laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) methods were applied for element and pigment concentration detection of marine water and phytoplankton samples. The spectra of plasmas generated by focusing the first harmonic λ = 1064 nm of a pulsed Nd:YAG laser on the liquid surfaces and phytoplankton samples in atmospheric pressure are described. Some of the chemical elements detecting by LIBS in the marine water (Na, Ca, Mg) and phytoplankton (Mg, Ca, Na, Fe, Si, Al) were defined. The radiation of second harmonic λ = 1064 nm of a pulsed Nd:YAG laser was used for phytoplankton pigments and dissolved organic matter detection by LIF. The results of joint application of LIBS and LIF measurements for phytoplankton communities state investigations inside Okhotsk Sea are presented.

We report on experiments on the interaction of a gigawatt femtosecond laser pulse train with hanging isolated millimeter-sized water droplets. A transparent droplet experienced explosive boiling-up and emitted light in the visible spectrum as a result of laser-induced plasma formed inside the droplet volume. The droplet emission spectra showed remarkable broadening, depending on the laser power. The role of pulse self-phase modulation in measured spectral broadening when the pulse propagates through the droplet is discussed.