The opportunities of the filament - induced emission spectroscopy method for analysis of elemental composition of aqueous aerosols in the atmosphere are estimated. Emission lines of chemical elements were excited by filamentation of femtosecond laser pulses (60 fs, 800 nm, 4.4 mJ) in the weak focus mode with the lens with 500 mm focal length in the aqueous aerosol. The limits of detection of aluminum, barium, and sodium in the aqueous aerosol are obtained.
The dependences of the intensity of sodium emission lines on the time delay during filamentation of laser radiation of femtosecond duration in an aqueous aerosol with large (10 μm) and small (0.8-2 μm) particles was obtained. Emission lines (588.99 and 589.59 nm) were excited by filamentation of femtosecond laser pulses (60 fs, 800 nm, 3.8 mJ) in the weak focus mode with the lens with 500 mm focal length in the Na aqueous aerosol. It was experimentally established the optimal time delay for recording of the emission spectra of the filament in an aqueous aerosol with respect to the laser pulse.
Emission spectra were obtained for various types of aerosol: aqueous (distilled water, NaCl aqueous solution, seawater aerosol), dust aerosol (aqueous solution of silicon nanoparticles, aqueous solution of atmospheric dust of various concentrations), and the elemental and molecular lines common for these types of aerosol were compared. Experimental data on the elemental composition of water aerosol were obtained by the method of filament-induced emission spectroscopy.
The compact mobile hardware-software complex based on a remotely operated vehicle (ROV) and a laser-induced breakdown spectrometer (LIBS) has been developed and tested in laboratory and in real-time condition for the tasks of analyzing the composition of sea water and bottom sediments on the continental shelf.
The limit of detection for Mg, Mn, Sr, B was experimentally investigated depending on the laser pulse repetition rate in the time resolved femtosecond LIBS. Optical breakdown on the surface of aqueous solutions was generated by the femtosecond Ti:Sa laser with the following parameters: central wavelength - 800 nm, pulse width - 60 fs, pulse energy - 1 mJ, repetition rate 50 Hz, 166 Hz, 250 Hz, 500 Hz, 1000 Hz. The best limit of detection was obtained for the 166 Hz laser repetition rate and for the following elements Mg I (285.2 nm), Mn I (403 nm, 403.3 nm), B I (283.2 nm), Sr I (460.7 nm) are 0.058, 0.025, 1.13, 4.69-3 mg/kg respectively.
The spectral and temporal characteristics of plasma radiation generated by a Ti:Sa femtosecond laser pulses on the surface of Ca aqueous solutions are investigated. Optimum parameters of laser radiation and signal registration are determined to improve the metrological characteristics of time-resolved femtosecond laser induced breakdown spectroscopy.
The spectral and temporal characteristics of plasma radiation (contours and kinetics of the intensity of spectral lines) generated by a Ti:Sa femtosecond laser pulses on the surface of water solutions are investigated. The best parameters of optical spectra registration and of the laser radiation are determined to improve the metrological characteristics of timeresolved femtosecond laser induced breakdown spectroscopy.
Experimental studies have been carried out to determine the limits of the detection of chemical elements (manganese, magnesium, lead, strontium) in water, when plasma generated by femtosecond laser pulses on the aqueous solutions surface, depending on the parameters of laser radiation (pulse duration, energy and the mode of focusing). The emission lines of chemical elements in plasma generated in a aqueous solution by Ti-Sapphire laser complex at a central wavelength of 800 nm, using focusing lenses with different focal lengths, and also for collimated beams under laboratory conditions are registered.
The results of lidar sensing of the atmosphere in the continent-ocean transition zone obtained on three modifications of a femtosecond lidar: elastic scattering lidar, Raman lidar, white light lidar are discussed. In the mode of multi-frequency sensing (supercontinuum from the fundamental harmonic), the emission lines of the first positive system of the nitrogen molecule are registered. Comparisons of obtained data with the results of lidar sensing using of nanosecond laser pulses are presented.
Time-resolved laser-induced breakdown spectroscopy (LIBS) has been used as an analytical chemistry technique suitable for water analysis. Optical breakdown on the surface of water solutions was generated by the femtosecond Ti:Sa laser with the following parameters: central wavelength - 800 nm, pulse width - 60 fs, pulse energy - 1 mJ, repetition rate 50 Hz, 166 Hz, 250 Hz, 500 Hz, 1000 Hz. The limit of detection (LOD) for Mg I (285.2 nm), Mn I (403 nm, 403.3 nm), Pb I (283.3 nm), Sr I (460.7 nm) was experimentally investigated depending on the laser pulse repetition rate by the time resolved femtosecond LIBS. The best LODs for Mg I - 0.058 mg/kg, Mn I - 0.025 mg/kg, Pb I - 0.711 mg/kg, Sr I - 4.69x10-3 mg/kg water solutions were obtained for 166 Hz repetition rate.
The developed underwater laser induced breakdown spectrometer consists of two units: 1- remotely operated vehicle (ROV) with the next main characteristics: work deep – up to 150 meters, maximum speed of immersion 1 m/s, maximum cruise velocity - 2 m/s and 2 – spectrometer unit (SU) consist of a DPSS Nd: YAG laser excitation source (double pulse with 50 mJ energy for each pulse at wavelength 1064 nm, pulse width 12 ns and pulse repetition rate 1-15 Hz, DF251, SOL Instruments), a spectrum recording system (Maya HR4000 or 2000 Pro spectrometer, Ocean Optics) and microcomputer. These two units are connected by Ethernet network and registered spectral data are automatically processed in a MATLAB platform.
Experimentally investigated limit of detection Mg, Al, Sr, Pb. depending on the pulse repetition rate femtosecond Ti: Sa laser optical breakdown in aqueous solutions on the surface of the investigated element in the laser pulse duration 60 fs, pulse energy of 1 mJ. The study was conducted for the laser pulse repetition rate of 50 Hz, 150 Hz, 250 Hz. To choose the optimal time delay of registration relative to the laser beam for the following chemicals Na, N, Fe, Ca, Mg, Al, Pb, Mn.
Experimentally determined the influence of energy and pulse repetition rate of the femtosecond Ti: sapphire laser on the intensity of the spectral lines in the optical breakdown on the surface of an aqueous solution of CaCl2 and aqueous solutions of iron. The time dependence of the intensity of the continuous and line spectra of the plasma was obtained from the laser pulse energy. It is shown that by increasing the laser pulse repetition frequency from 20 Hz to 1000 Hz is observed up to 45% reduction of the emission line intensity Ca II (393.3 nm).
Created three modifications lidar systems based on Ti: sapphire laser with chirped power amplification (elastic scattering lidar, Raman lidar, white light lidar) and derived atmospheric lidar sensing data in a transition zone continent-ocean. Comparisons of the data with the results of conventional lidar based on the use of nanosecond laser pulses are presented. Possibilities and prospects created by femtosecond lidar modifications in the conditions of the transition zone continentocean.
The spectral lines broadening in femtosecond laser plasma generated by the 45 fs Ti:Sa laser pulses on the surface of the water solutions of Ba is investigated. The contribution of the Doppler broadening for spectral lines width is minimal and amounts 0.0022 nm for Ba. The main mechanism of Ba spectral line broadening in experimental conditions is resonance. The resulting values of resonance broadening constitute a 0.0349 nm for Ba I (413.24 nm), 0.0563 nm for Ba I (553.54 nm), 0.0241 nm for Ba II (455.41 nm), 0.0437 nm for Ba II (614.17 nm).
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