Evaluation of self-absorption of manganese emission lines in Laser Induced Breakdown Spectroscopy measurements

This paper is part of a more general study aimed to the determination of the best experimental procedures for reliable quantitative measurements of Fe-Mn alloys by LIBS. In this work, attention is pointed on the self-absorption processes, whose effect deeply influences the LIBS measurements, reflecting in non-linear calibration curves. The effect of self-absorption on the line intensity can be quantified by defining a self absorption coefficient, that measures the deviation of the line intensity from the linear extrapolation of the curve of growth in the optically thin regime. The authors demonstrated in a previous paper that self absorption coefficients could be calculated once the electron density of the plasma is known and the Stark coefficients of the lines are available. However, when the Stark coefficients of the lines of interest are not known, a different approach is needed. In this work a new method for evaluation of self absorption coefficients in LIBS measurements is presented, which does not require the knowledge of Stark coefficients. In order to understand the basic principles and setting out the theoretical tools that will be used for the analysis o f the alloys, a preliminary study was done on pure Mn; LIBS spectra were acquired in different experimental conditions, at different laser energies and different delays after the laser irradiation o f the sample. Moreover, collinear double pulse measurements were also performed. Analytical relations were derived and experimental procedures devised for evaluation o f the self absorption coefficients of several Mn lines, which are important for characterization and control of the experimental conditions in which the analysis is performed

Determination of velocity profiles in pipes by a pulsed photoacoustic method

The present work describes the development of a pulsed photoacoustic (PA) flowmeter. An acoustic wave in a flowing fluid is produced by absorption of a laser pulse focused over a path flow line. The acoustic propagations, along and against the flow, are monitored by two cw probe beams. In the interaction, the probe beam undergoes a transient deflection that is detected by a fast response photodiode (PD). Measurements of the acoustic arrival time through the pipe cross section are acquired. The velocity distribution data profile of a square pipe is obtained applying the cylindrical shockwave model developed by Vlasses and the velocity equation established in an earlier work by Zapka and Tam [9]. The profiles determined with this method are fixed through two turbulent pipe flow models, showing good agreement

The evolution of the longitudinal modulus during the photo-polymerisation of a bis-GMA/TEGDMA resin by pulsed photoacoustic technique

A pulsed photoacoustic (PA) technique was implemented to study the evolution of the longitudinal modulus, $C_{11}$, during the polymerisation of a methacrylate co-monomer system, induced by UV light. A laser pulse was used as a standard source of ultrasound waves to monitor the changes in the longitudinal velocity of the acoustic signal during the photo-polymerisation (PP) a bis-GMA/TEGDMA co-monomer system (70/30 %w/w) containing camphorquinone as photo-initiator, and N,N-dimethyl-p-toluidine as reducing agent. $C_{11}$ was determined on real time conditions after irradiating the system for predetermined periods. The kinetics of the PP reaction was also studied by infrared spectroscopy in order to compare the evolution of $C_{11}$ with the rate of conversion of the double bounds of the methacrylate groups. The evolution of $C_{11}$ reflects the whole polymerisation process: The technique permits to determine the transitions of the resin during polymerisation from viscous to viscoelastic state and further to a glassy polymer

Trace analysis of pesticides in water using pulsed photoacoustic technique

Trace concentration of pesticides such as Atrazine and Methyl parathion in water solutions has harmful health effects. In this work a methodology to detect trace concentrations for both pesticides has been developed. The pesticide solution contained into a quartz cell is irradiated by a pulsed laser at λ = 230 nm, this energy is absorbed depending on the pesticide concentration; the non absorbed light that sample allows to pass is absorbed by the NaCl:Mn2+ doped single crystal fixed to a piezoelectric sensor of 5 MHz to obtain the photo- acoustic (PA) signal. The results showed that is possible to detect concentrations around tenths of ng/l

A new procedure for estimating the temperature and the departure of the LTE condition in a time-dependent plasma

This paper presents a method for estimating the temperature of transient plasmas and their degree of departure of the LTE condition. This method is based on the application of the Boltzmann and Saha equations on the temporal variation of the intensity of the spectral lines of the plasma, under the assumption that the plasmas at the different times where the spectra were obtained are in Local thermal Equilibrium. The method does not require the knowledge of the spectral efficiency of the spectrometer/detector, of the transition probabilities of the lines considered or the degeneracies of the upper and lower levels. Provided that the conditions of optically thin, homogeneous plasma in LTE are fulfilled, the only limiting factor to the accuracy of the method is the precision in determining the line intensity at the two temperatures Ta and Tb considered. The method also proposes a relation between plasma temperature and electron number density which could be used for determining deviations from ideal plasma conditions in Laser-Induced Breakdown Spectroscopy (LIBS) experiments.Fil: Bredice, Fausto Osvaldo. Consejo Nacional de Invest.cientif.y Tecnicas. Centro Cientifico Tecnol.conicet - la Plata. Centro de Invest.opticas (i); Argentina;Fil: Borges, F.. Universidad Federal Fluminense; Brasil;Fil: Di Rocco, Hector Omar. Consejo Nacional de Invest.cientif.y Tecnicas. Centro Cientifico Tecnol.conicet - la Plata. Centro de Invest.opticas (i); Argentina;Fil: Sarmiento Mercado, Rafael. Universidad Nacional del Centro de la Provincia de Bs.as.. Facultad de Cs.exactas. Instituto de Fisica Arroyo Seco;Fil: Villagrán-Muniz, M.. Universidad Nacional Autónoma de México. Centro de Ciencias Aplicadas y Desarrollo Tecnológica. . Laboratorio de Fotofísica. Centro de Ciencias Aplicadas y Desarrollo Tecnológica; Argentina

Temporal analysis of self-reversed Ag I resonant lines in LIBS experiment at different laser pulse energy and in different surrounding media

In this work we studied the temporal evolution of the resonant emission lines of neutral silver (Ag I) at wavelengths328.9 nm and 338.2 nm, in different surrounding media (He, Ar, Xe and air) and at different laser pulseenergy (15 mJ, 30 mJ and 60 mJ), using a frequency triplicated Nd:YAG laser (355 nm).We observed that the self-reversal of the Ag lines, caused by the combined effect of self-absorption and plasmainhomogeneity, is strong when the plasma expands in molecular gases (N2 and O2 in air) while is negligible inatomic noble gases (He, Ar, Xe), independently on the mass of the atoms. From the experimental data, we alsoconclude that the shock wave generated during the breakdown may play an important role in generating theplasma inhomogeneities which are essential conditions for the occurrence of the self-reversal effect.Fil: Urbina Medina, Ivan Alexander. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Ópticas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones Ópticas. Universidad Nacional de La Plata. Centro de Investigaciones Ópticas; ArgentinaFil: Bredice, Fausto Osvaldo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Investigaciones Ópticas. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Investigaciones Ópticas. Universidad Nacional de La Plata. Centro de Investigaciones Ópticas; ArgentinaFil: Sanchez Aké, C.. Universidad Nacional Autónoma de México; MéxicoFil: Villagrán Muniz, M.. Universidad Nacional Autónoma de México; MéxicoFil: Palleschi, V.. No especifíca

A New Method for Determination of Self-Absorption Coefficients of Emission Lines in Laser-Induced Breakdown Spectroscopy Experiments

In this paper we present a new method for determining the self-absorption coefficients of emission lines in laser-induced breakdown spectroscopy (LIBS) experiments. With respect to other methods already present in the literature, the proposed approach has the advantage of not requiring, providing some conditions are fulfilled, any knowledge of the plasma parameters such as temperature and electron number density and of the emission line spectral coefficients such as transition probability. An example of the application of the approach is given for emission lines measured at different delay times after laser ablation of a silver target.Fil: Bredice, Fausto Osvaldo. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Exactas. Instituto de Física Arroyo Seco; ArgentinaFil: Di Rocco, Hector Omar. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Tandil. Sede Tandil del Centro de Investigaciones En Fisica E Ingenieria del Centro de la Provincia de Buenos Aires; ArgentinaFil: Sobral, Hugo M.. No especifíca;Fil: Villagrán-Muniz, Mayo. No especifíca;Fil: Palleschi, Vincenzo. No especifíca