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 dynamics of spectral components arising in the time interval up to 15 ns after the main femtosecond pulse is investigated for filamentation of tightly focused laser radiation. The femtosecond pulse duration was 65 fs, the main pulse energy increased from 0.5 to 1.7 mJ. Several spectral components of laser emission in the wavelength range of 720–780 nm are registered. With increase of main pulse energy, the shape of the spectrum of the supercontinuum changes, the intensity of the post-pulse and the amplified spontaneous emission increases, and a shift of the component to the blue region is observed. It is assumed that the component whose central wavelength shifts to the blue region with is associated with Rabi splitting of the oxygen atom levels.
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 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.
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 temporal evolution of intensity of N2 337 nm and N2+ 391.2 nm lines is compared with modeling results for filament plasma produced by tightly focused femtosecond laser pulse (0.9 mJ, 48 fs). Model correctly predicts enhanced emission of 1+ system, higher intensity of O I 777.4 nm line and dynamics of excited states density.
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.
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 temporal evolution of width and shift of N I 746.8 and O I 777.4 nm lines is investigated in filament plasma produced by tightly focused femtosecond laser pulse (0.9 mJ, 48 fs). Nitrogen line shift is determined by joint action of electron impact shift and far-off resonance AC Stark effect. Intensive (I ~ 1010 W/cm2 ) electric field of ASE and postpulses result in possible LS coupling break for O I 3p 5P level and generation of Rabi sidebands. The blue-shifted main femtosecond pulse and Rabi sideband cause the stimulated emission of N21+ system.
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.
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).
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).
The influence of pulse energy on the time evolution of the intensity of the continuum and emission lines of plasma generated on the surface of aqueous solutions of iron by focused radiation Ti: sapphire laser with a wavelength of 800 nm and pulse duration of 45 fs and a range of energy 3-7 mJ was investigated. The calibration curve for iron in water and 3-ó limit of detection of iron in water was obtained.
The energy absorbed by femtosecond laser plasma has nonlinear dependence on incident laser energy. The threshold power for plasma formation is 5.2 GW. Emission of nitrogen molecule, nitrogen molecule ion, atomic oxygen (unresolved triplet O I 777 nm) and nitrogen (triplet N I 742.4, 744.3 and 746.8 nm) lines is detected. Molecular emission consists of second positive and firs negative systems of nitrogen. Time-resolved spectroscopy of plasmas shows short molecular line emission (up to 1 ns) and long atomic line emission (up to 150 ns).
The Raman spectra of femtosecond laser pulses in distilled and tap water, and luminescence spectra of aqueous solutions containing dissolved organic matter, chlorophyll "a" and biological objects excited by ultra-short laser pulses was investigated.
It’s shown that the increasing of electron impact excitation rate constant lead to increasing of line intensity, so the limit of detection (LOD) is lower. For femtosecond laser plasma generated on the sea water surface, the relation of the detection limits will be LOD(Na) < LOD(Ca) < LOD(Mg). The fact that the atomic line of Ca I 422 nm is more sensitive for femtosecond laser-induced breakdown spectroscopy is described.
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.
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.
Mechanisms of absorption wave of laser radiation and spectral characteristics of laser plasma were investigated at a laser breakdown in a normal atmosphere. Q-switched Nd:YAG laser operated at 1064 and 532 nm were used in experiment. Laser pulse consisted of prepulse and basic pulse for both laser wavelengths. Time interval between pulses was 15 ns, time duration (FWHM) was 4 ns for 532 nm wavelength, 5 ns for 1064 nm wavelength. Molecular emission and collapse of intensity of plasma continuum during the initial moments of laser plasma expansion were registered. It was carried out examination of colliding plasmas interaction which depended on absorption wave mechanism and distance between focal points of lens. The magnification of integrated intensity in case of plasmas interaction is registered. Decay time of continuous spectrum and lines emission was increased thus contrast of emission lines was also increased.
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.
The Laser-Induced Breakdown Spectroscopy (LIBS) method was applied for detection of phytoplankton and marine water elemental composition. The results of the sea water quality monitoring and phytoplankton element composition measuring obtained in the Okhotsk coastal sea water during scientific research expedition in 2000-2001 years are described.
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.
Laser plasma generated on the surface of solid targets located in gas atmosphere leads to the formation of a strong shock wave, which changes thermodynamic and spectral plasma characteristics accompanied by Stark effect. The registration of Stark shift and broadening of emission spectral lines allowed us to determine electron temperature and electron density for the ambient gas pressure range of 200 - 1200 Torr without considering presence of local thermodynamic equilibrium in the studied volume of aluminum plasma. The electron temperature and density of plasma increased along with gas pressure, which was explained by the formation of the more intensive shock wave. The velocity of laser plasma expansion in vacuum was obtained by measuring Doppler shift of weakly broadened lines of emission spectra, collected at two different angles from the normal of target surface. The measurement of line broadening, caused by square Stark effect, gave us an estimate of electric field in aluminum plasma. For Q- switched Nd:YAG laser operating at a 1.064-micrometers wavelength with a pulse energy of 0.6 J and a time duration of the laser pulse of 20 ns, the electric field in the studied plasma volume was 18 kV/cm for ambient gas (helium) pressure of 760 Torr.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.