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  • 1
    Online Resource
    Online Resource
    Formation of a Cesium Plasma by Continuous-Wave Resonance Excitation
    SAGE Publications ; 2000
    In:  Applied Spectroscopy Vol. 54, No. 8 ( 2000-08), p. 1245-1249
    Details
    In: Applied Spectroscopy, SAGE Publications, Vol. 54, No. 8 ( 2000-08), p. 1245-1249
    Abstract: The generation of a plasma in cesium vapor via a resonance process is described. The maximum irradiance used was 1.5 W/cm2, which is several orders of magnitude lower than the irradiances conventionally used to form plasmas. Plasma emission consisted of radiative decay from excited-state Cs atoms. Optical emission from the plasma was observed from laser powers of 200 μW with a nonintensified charge-coupled device (CCD). The ionization efficiency of the plasma was approximately 0.001, with the majority of the atoms in the plasma ionized. The plasma was found to behave linearly with respect to laser power; however nonlinear behavior was observed as the number density was altered. A collisional mechanism is proposed for the formation of the plasma.
    Type of Medium: Online Resource
    ISSN: 0003-7028 , 1943-3530
    URL: Article
    DOI: 10.1366/0003702001950841
    RVK:
    VA 2367
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2000
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  • 2
    Online Resource
    Online Resource
    Laser-Induced Breakdown Spectroscopy (LIBS), Part I: Review of Basic Diagnostics and Plasma—Particle Interactions: Still-Challenging Issues within the Analytical Plasma Community
    SAGE Publications ; 2010
    In:  Applied Spectroscopy Vol. 64, No. 12 ( 2010-12), p. 335A-336A
    Details
    In: Applied Spectroscopy, SAGE Publications, Vol. 64, No. 12 ( 2010-12), p. 335A-336A
    Abstract: Laser-induced breakdown spectroscopy (LIBS) has become a very popular analytical method in the last decade in view of some of its unique features such as applicability to any type of sample, practically no sample preparation, remote sensing capability, and speed of analysis. The technique has a remarkably wide applicability in many fields, and the number of applications is still growing. From an analytical point of view, the quantitative aspects of LIBS may be considered its Achilles' heel, first due to the complex nature of the laser–sample interaction processes, which depend upon both the laser characteristics and the sample material properties, and second due to the plasma–particle interaction processes, which are space and time dependent. Together, these may cause undesirable matrix effects. Ways of alleviating these problems rely upon the description of the plasma excitation-ionization processes through the use of classical equilibrium relations and therefore on the assumption that the laser-induced plasma is in local thermodynamic equilibrium (LTE). Even in this case, the transient nature of the plasma and its spatial inhomogeneity need to be considered and overcome in order to justify the theoretical assumptions made. This first article focuses on the basic diagnostics aspects and presents a review of the past and recent LIBS literature pertinent to this topic. Previous research on non-laser-based plasma literature, and the resulting knowledge, is also emphasized. The aim is, on one hand, to make the readers aware of such knowledge and on the other hand to trigger the interest of the LIBS community, as well as the larger analytical plasma community, in attempting some diagnostic approaches that have not yet been fully exploited in LIBS.
    Type of Medium: Online Resource
    ISSN: 0003-7028 , 1943-3530
    URL: Article
    DOI: 10.1366/000370210793561691
    RVK:
    VA 2367
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2010
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  • 3
    Online Resource
    Online Resource
    Laser-Induced Breakdown Spectroscopy Combined with Spatial Heterodyne Spectroscopy
    SAGE Publications ; 2014
    In:  Applied Spectroscopy Vol. 68, No. 9 ( 2014-09), p. 1076-1084
    Details
    In: Applied Spectroscopy, SAGE Publications, Vol. 68, No. 9 ( 2014-09), p. 1076-1084
    Abstract: A spatial heterodyne spectrometer (SHS) is tested for the first time in combination with laser-induced breakdown spectroscopy (LIBS). The spectrometer is a modified version of the Michelson interferometer in which mirrors are replaced by diffraction gratings. The SHS contains no moving parts and the gratings are fixed at equal distances from the beam splitter. The main advantage is high throughput, about 200 times higher than that of dispersive spectrometers used in LIBS. This makes LIBS-SHS a promising technique for low-light standoff applications. The output signal of the SHS is an interferogram that is Fourier-transformed to retrieve the original plasma spectrum. In this proof-of-principle study, we investigate the potential of LIBS-SHS for material classification and quantitative analysis. Brass standards with broadly varying concentrations of Cu and Zn were tested. Classification via principal component analysis (PCA) shows distinct groupings of materials according to their origin. The quantification via partial least squares regression (PLS) shows good precision (relative standard deviation 〈 10%) and accuracy (within ± 5% of nominal concentrations). It is possible that LIBS-SHS can be developed into a portable, inexpensive, rugged instrument for field applications.
    Type of Medium: Online Resource
    ISSN: 0003-7028 , 1943-3530
    URL: Article
    DOI: 10.1366/14-07544
    RVK:
    VA 2367
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2014
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  • 4
    Online Resource
    Online Resource
    Diagnostic of Laser-Induced Plasma Using Abel Inversion and Radiation Modeling
    SAGE Publications ; 2013
    In:  Applied Spectroscopy Vol. 67, No. 8 ( 2013-08), p. 851-859
    Details
    In: Applied Spectroscopy, SAGE Publications, Vol. 67, No. 8 ( 2013-08), p. 851-859
    Abstract: A method based on matching synthetic and experimental emissivity spectra was applied to spatially resolved measurements of a laser-induced plasma ignited in argon at atmospheric pressure. The experimental emissivity spectra were obtained by Abel inversion of intensity spectra measured from a thin plasma slice perpendicular to the plasma axis. The synthetic spectra were iteratively calculated from an equilibrium model of plasma radiation that included free–free, free–bound, and bound–bound transitions. From both the experimental and synthetic emissivity spectra, spatial and temporal distributions of plasma temperature and number densities of plasma species (atoms, ions, and electrons) were obtained and compared. For the best-fit synthetic spectra, the temperature and number densities were read directly from the model; for experimental spectra, these parameters were obtained by traditional Boltzmann plot and Stark broadening methods. In both cases, the same spectroscopic data were used. Two approaches revealed a close agreement in electron number densities, but differences in plasma excitation temperatures and atom number densities. The trueness of the two methods was tested by the direct Abel transform that reconstructed the original intensity spectra for comparing them to the measured spectra. The comparison yielded a 9 and 13% difference between the reconstructed and experimental spectra for the numerical and traditional methods, respectively. It was thus demonstrated that the spectral fit method is capable of providing more accurate plasma diagnostics than the Boltzmann plot and Stark broadening methods.
    Type of Medium: Online Resource
    ISSN: 0003-7028 , 1943-3530
    URL: Article
    DOI: 10.1366/12-06929
    RVK:
    VA 2367
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2013
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  • 5
    Online Resource
    Online Resource
    Analysis of Sulfuric Acid Aerosols by Laser-Induced Breakdown Spectroscopy and Laser-Induced Photofragmentation
    SAGE Publications ; 2000
    In:  Applied Spectroscopy Vol. 54, No. 12 ( 2000-12), p. 1805-1816
    Details
    In: Applied Spectroscopy, SAGE Publications, Vol. 54, No. 12 ( 2000-12), p. 1805-1816
    Abstract: Laser-induced breakdown spectroscopy and laser photofragmentation spectroscopy are investigated as potential approaches to the detection and quantification of the sulfuric acid aerosols resulting from the oxidation of dimethylsulfide in air. The former, direct technique, where aerosols are introduced in the plasma formed by focusing the fundamental frequency of a Nd:YAG laser in air, and atomic sulfur emission is measured in the region 180 nm, gives a limit of detection of 165 ppbv for a 15 min integration time, which is inadequate for our purposes. The second, indirect approach, based on the photofragmentation, with 193 nm photons, of the compound resulting from interaction between sodium chloride and sulfuric acid aerosols, gives a detection limit of 46.5 ppbv in 10 s measuring time. With this method, a complete “titration curve” for sulfuric acid aerosols can be obtained in “quasi” real-time.
    Type of Medium: Online Resource
    ISSN: 0003-7028 , 1943-3530
    URL: Article
    DOI: 10.1366/0003702001948907
    RVK:
    VA 2367
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2000
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  • 6
    Online Resource
    Online Resource
    Laser Spark Ignition of Premixed Methane–Air Mixtures: Parameter Measurements and Determination of Key Factors for Ultimate Ignition Results
    SAGE Publications ; 2014
    In:  Applied Spectroscopy Vol. 68, No. 9 ( 2014-09), p. 975-991
    Details
    In: Applied Spectroscopy, SAGE Publications, Vol. 68, No. 9 ( 2014-09), p. 975-991
    Abstract: In this study, we present an experimental investigation of the parameters of the laser spark ignition of premixed methane–air mixtures and the determination of the key factors for the ultimate ignition result. Ignition is achieved in a mesh honeycomb burner using the 1064 nm output of a neodymium-doped yttrium aluminum garnet (Nd : YAG) laser. All pertinent laser ignition parameters, including the minimum ignition energy, the ignition time and blow out time, and the effects that the variation of experimental conditions, such as the spark energy, ignition position, equivalence ratio (ER), and flow rate, have on these parameters have been addressed systematically. To identify the key factors for the ultimate result of laser ignition, several parameters of the ignition processes are measured simultaneously, with an emphasis given to the temporal behavior of the hydroxyl (OH) radicals in relation to the data regarding the spark energy and the local ER. A clear finding of the study is that successful ignition events are always related to higher OH radical photon emissions, considered to be proportional to the concentration level of the OH radicals present, thus indicating a direct link between the OH level at early times (on a microsecond scale) and the ultimate result of laser ignition. Two-dimensional correlation plots of the spark energy, local ER, and OH radical photon count at early times with the ultimate results of laser ignition indicate that the spark energy and local ER do not play a critical role in determining the success or failure of the ignition and that the OH concentration in the early time range is the key factor in determining the final fate of laser ignition. Finally, on the basis of the results obtained here and in the existing literature, some considerations of the mechanism of laser ignition are presented.
    Type of Medium: Online Resource
    ISSN: 0003-7028 , 1943-3530
    URL: Article
    DOI: 10.1366/13-07356
    RVK:
    VA 2367
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2014
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  • 7
    Online Resource
    Online Resource
    Experimental Investigation of Sodium Emission following Laser Photofragmentation of Different Sodium-Containing Aerosols
    SAGE Publications ; 2001
    In:  Applied Spectroscopy Vol. 55, No. 7 ( 2001-07), p. 809-815
    Details
    In: Applied Spectroscopy, SAGE Publications, Vol. 55, No. 7 ( 2001-07), p. 809-815
    Abstract: Several time-integrated and time-resolved experiments have been performed on different sodium-containing dry aerosols in air to investigate the behavior of atomic sodium emission at the yellow doublet after photofragmentation with 193 nm photons provided by an ArF excimer laser. It is shown that sodium chloride, sodium hydroxide, and especially sodium sulfate require different thresholds for the overall process of vaporization, dissociation, and excitation of atomic emission. This can be clearly seen by the experimental fact that (1) the onset of the time-integrated emission signal starts at different laser energies, and (2) the time-resolved shapes of the emission signal during the laser pulse (13 ns) are markedly different in the case of chloride and sulfate aerosols, the former rising faster than the latter. From an analytical point of view, the detection limit for sodium in airborne particles is 0.3 ng of sodium per gram of air (∼ 0.017 ppbv), which is about one order of magnitude better than the detection limit reported by early laser-induced plasma experiments.
    Type of Medium: Online Resource
    ISSN: 0003-7028 , 1943-3530
    URL: Article
    DOI: 10.1366/0003702011952640
    RVK:
    VA 2367
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2001
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  • 8
    Online Resource
    Online Resource
    Detecting Temporal Changes of Self-Absorption in a Laser-Induced Copper Plasma from Time-Resolved Photomultiplier Signal Emission Profiles
    SAGE Publications ; 2019
    In:  Applied Spectroscopy Vol. 73, No. 2 ( 2019-02), p. 163-170
    Details
    In: Applied Spectroscopy, SAGE Publications, Vol. 73, No. 2 ( 2019-02), p. 163-170
    Abstract: This work reports an investigation on the feasibility of using a photomultiplier tube (PMT) to follow the time evolution of self-absorption of copper resonance transitions at 324.7 nm and 327.4 nm. The plasma was obtained by focusing a Nd:YAG laser, operated at 1064 nm, on a series of aluminum alloy standard disks containing different copper concentrations. The results described have been obtained at different times and with different set-ups. These set-ups consisted of a Paschen–Runge polychromator, a LIBS 2000 spectrometer, and a spectrometer equipped with both an intensified charge-coupled device (ICCD) and PMT. Both PMT signals and time-resolved spectra were obtained and the ratio of the two Cu resonant lines was calculated, compared, and discussed. By selecting different delay times and integration gates of the PMT signals, the self-absorption effect of the Cu resonant lines was found to be changing, implying that, by careful selection of the integration window of PMT signals, the self-absorption may be minimized, thus improving the calibration linearity of the technique.
    Type of Medium: Online Resource
    ISSN: 0003-7028 , 1943-3530
    URL: Article
    DOI: 10.1177/0003702818812087
    RVK:
    VA 2367
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2019
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  • 9
    Online Resource
    Online Resource
    Single Particle Fluorescence: A Simple Experimental Approach to Evaluate Coincidence Effects
    SAGE Publications ; 2007
    In:  Applied Spectroscopy Vol. 61, No. 7 ( 2007-07), p. 711-718
    Details
    In: Applied Spectroscopy, SAGE Publications, Vol. 61, No. 7 ( 2007-07), p. 711-718
    Abstract: Real-time characterization of the chemical and physical properties of individual aerosol particles is an important issue in environmental studies. A well-established way of accomplishing this task relies on the use of laser-induced fluorescence or laser ionization mass spectrometry. We describe here a simple approach aimed at experimentally verifying that single particles are indeed addressed. The approach has been tested with a system consisting of a series of aerodynamic lenses to form a beam of dye-doped particles aerosolized from a solution of known concentration with a medical nebulizer. Two independent spectral detection channels simultaneously measure the fluorescence signals generated in two different spectral regions by the passage of a mixture of two dye-doped particles through a focused laser beam in a vacuum chamber. Coincidence effects, arising from the simultaneous observation of both fluorescence emissions, can then be directly observed. Both dual-color fluorescence and pulse height distribution have been analyzed. As expected, the probability of single- or multiple-particle interaction strongly depends on the particle flux in the chamber, which is related to the concentration of particles in the nebulized solution. In our case, to achieve a two-particle coincidence smaller than 10%, a particle concentration lower than 1.2 × 10 5 particles/mL is required. Moreover, it was found that the experimental observations are in agreement with a simple mathematical model based on Poisson statistics. Although the results obtained refer to particle concentrations in solution, our approach can equally be applicable to experiments involving direct air sampling, provided that the number density of particles in air can be measured a priori, e.g., with a particle counter.
    Type of Medium: Online Resource
    ISSN: 0003-7028 , 1943-3530
    URL: Article
    DOI: 10.1366/000370207781393424
    RVK:
    VA 2367
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2007
    detail.hit.zdb_id: 1474251-2
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  • 10
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    Online Resource
    Absorption Spectrometry by Narrowband Light in Optically Saturated and Optically Pumped Collision and Doppler Broadened Gaseous Media under Arbitrary Optical Thickness Conditions
    SAGE Publications ; 2006
    In:  Applied Spectroscopy Vol. 60, No. 11 ( 2006-11), p. 1217-1240
    Details
    In: Applied Spectroscopy, SAGE Publications, Vol. 60, No. 11 ( 2006-11), p. 1217-1240
    Abstract: This work examines absorption spectrometry by narrowband light in gaseous media with arbitrary optical thickness when the light induces optical saturation or optical pumping. Two quantities are defined: the observed absorbance, A obs , and the true absorbance, A true . The former is the absorbance that is measured under the existing conditions, whereas the latter represents the absorbance one would measure if the light acted solely as a probe of the populations of the various levels, and it is therefore directly proportional to the concentration or density of absorbers. A general integral equation for the propagation of light in media of arbitrary optical thickness in which the light influences the populations of the levels involved is derived. This expression is transcendental in the observed absorbance and cannot be solved analytically. It is shown that an analytical expression can be derived by investigating the inverse relationship, i.e., A true = f ( A obs ). Inasmuch as collision and Doppler broadened media react differently to optical saturation, they are considered separately. It is shown that a nonlinear response results if the medium is optically saturated (or pumped) and not optically thin. Expressions for the error introduced if the technique of standard additions is uncritically applied to such a system are derived.
    Type of Medium: Online Resource
    ISSN: 0003-7028 , 1943-3530
    URL: Article
    DOI: 10.1366/000370206778999049
    RVK:
    VA 2367
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2006
    detail.hit.zdb_id: 1474251-2
    SSG: 11
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