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Sökning: L773:0003 7028 OR L773:1943 3530

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1.
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2.
  • Aldén, Marcus, et al. (författare)
  • Application of Cars Spectroscopy To the Detection of So2
  • 1988
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 42:8, s. 1421-1427
  • Tidskriftsartikel (refereegranskat)abstract
    • Experiments have been performed to investigate the possibility of detecting low concentrations of SO2 using CARS spectroscopy. The experiments were also aimed at high-temperature investigations both in a heated cell and in a flame. During the cell measurements it was clearly revealed that the temperature has a dramatic influence on the shape of the CARS spectra, indicating a good potential for thermometry using SO2 and CARS spectroscopy.
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3.
  • Alwahabi, Z. T., et al. (författare)
  • Measurements of collisional broadening coefficients by infrared polarization spectroscopy
  • 2007
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 61:4, s. 424-427
  • Tidskriftsartikel (refereegranskat)abstract
    • We present measurements of collisional broadening coefficients, obtained at atmospheric pressure, by polarization spectroscopy. Using tunable single mode laser radiation at similar to 2 pro, high-resolution infrared polarization spectra were recorded for CO2-Ar and CO2-He binary mixtures. The recorded polarization spectra were fitted with a Lorentzian cubed function form to obtain the broadening coefficients. The full-width at half-maxima (FWHM) collisional broadening rates of CO2 by Ar and He, for the R14 (12(0)1 <- 00(0)0) line, have been determined to be 0.161 +/- 0.018 cm(-1) atm(-1) and 0.1823 +/- 0.0032 cm(-1) atm(-1), respectively.
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4.
  • Ankerst, J, et al. (författare)
  • Laser-induced Fluorescence Studies of Hematoporphyrin Derivative (hpd) In Normal and Tumor-tissue of Rat
  • 1984
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 38:6, s. 890-896
  • Tidskriftsartikel (refereegranskat)abstract
    • Fluorescence studies of hematoporphyrin derivative (HPD) in normal and tumor tissue of rat were performed with nitrogen laser excitation and optical multi-channel detection. Fifteen types of tissue including inoculated tumor were investigated for rats at different delays after HPD injection. Optimum contrast functions and other criteria for discriminating tumor tissue from normal tissue are discussed. The results should have implications for practical human HPD endoscopy.
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5.
  • Artesani, Alessia, et al. (författare)
  • Terahertz Time-Domain Spectroscopy in Reflection Configuration for Inorganic and Mineral Pigment Identification
  • 2023
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 77:1, s. 74-87
  • Tidskriftsartikel (refereegranskat)abstract
    • This work demonstrates terahertz time-domain spectroscopy (THz-TDS) in reflection configuration on a class of inorganic and mineral pigments. The technique is validated for pictorial materials against the limitations imposed by the back-reflection of the THz signal, such as weak signal intensity, multiple signal losses and distortion, as well as the current scarce databases. This work provides a detailed description of the experimental procedure and method used for the determination of material absorption coefficient of a group of 10 pigments known to be used in ancient frescoes, that are, Cu-based (azurite, malachite, and Egyptian blue), Pb-based (minium and massicot), Fe-based (iron oxide yellow, dark ochre, hematite, and Pompeii red) pigments and mercury sulfide (cinnabar), and classified the vibrational modes of the molecular oxides and sulfides for material identification. The results of this work showed that the mild signal in reflection configuration does not limit the application of THz-TDS on inorganic and mineral pigments as long as (i) the THz signal is normalized with a highly reflective reference sample, (ii) the secondary reflected signals from inner interfaces are removed with a filtering procedure, and (iii) the limitations at high frequencies imposed by the dynamic range of the instrument are considered. Under these assumptions, we were able to differentiate molecular phases of the same metal and identify azurite, Egyptian blue, minium, and cinnabar, isolating the molecular vibrations up to 125 cm−1. The established approach demonstrated to be reliable, and it can be extended for the study of other materials, well beyond the reach of the heritage domain. 
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6.
  • Artursson, Tom, et al. (författare)
  • Study of Preprocessing Methods for the Determination of Crystalline Phases in Binary Mixtures of Drug Substances by X-ray Powder Diffraction and Multivariate Calibration
  • 2000
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 54:8, s. 272A-301A
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, various preprocessing methods were tested on data generated by X-ray powder diffraction (XRPD) in order to enhance the partial least-squares (PLS) regression modeling performance. The preprocessing methods examined were 22 different discrete wavelet transforms, Fourier transform, Savitzky-Golay, orthogonal signal correction (OSC), and combinations of wavelet transform and OSC, and Fourier transform and OSC. Root mean square error of prediction (RMSEP) of an independent test set was used to measure the performance of the various preprocessing methods. The best PLS model was obtained with a wavelet transform (Symmlet 8), which at the same time compressed the data set by a factor of 9.5. With the use of wavelet and X-ray powder diffraction, concentrations of less than 10% of one crystal from could be detected in a binary mixture. The linear range was found to be in the range 10-70% of the crystalline form of phenacetin, although semiquantitative work could be carried out down to a level of approximately 2%. Furthermore, the wavelet-pretreated models were able to handle admixtures and deliberately added noise.
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7.
  • Axelsson, H, et al. (författare)
  • Differential Optical Absorption Spectroscopy (DOAS) Measurements of Ozone in the 280--290 nm Wavelength Region
  • 1990
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 44:10, s. 1654-1658
  • Tidskriftsartikel (refereegranskat)abstract
    • The differential absorption structure of the ozone spectrum between 250 and 330 nm has been investigated in order to determine the optimal wavelength region to be utilized for active differential optical absorption spectroscopy (DOAS) measurements. Considering aspects of atmospheric attenuation and interference from other species as well as the magnitude of the differential absorption cross section, an interval around 283 nm was found to be a good candidate for this application. This result was also verified during 12 months of continuous ozone monitoring in an urban environment.
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8.
  • Axelsson, H, et al. (författare)
  • Measurement of Aromatic-hydrocarbons With the DOAS Technique
  • 1995
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 49:9, s. 1254-1260
  • Tidskriftsartikel (refereegranskat)abstract
    • Long-path DOAS (differential optical absorption spectroscopy) in the ultraviolet spectral region has been shown to be applicable for low-concentration measurements of light aromatic hydrocarbons. However, because of spectral interferences among different aromatics as well as with oxygen, ozone, and sulfur dioxide, the application of the DOAS technique for this group of components is not without problems. This project includes a study of the differential absorption characteristics, between 250 and 280 nm, of twelve light aromatic hydrocarbons representing major constituents in technical solvents used in the automobile industry. Spectral overlapping between the different species, including oxygen, ozone, and sulfur dioxide, has been investigated and related to the chemical structure of the different aromatics. Interference effects in the DOAS application due to spectral overlapping have been investigated both in quantitative and in qualitative terms, with data from a field campaign at a major automobile manufacturing plant.
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9.
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10.
  • Axner, Ove, et al. (författare)
  • Absorption spectrometry by narrowband light in optically saturated and optically pumped collision and doppler broadened gaseous media under arbitrary optical thickness conditions
  • 2006
  • Ingår i: Applied Spectroscopy. - New York : Society for applied spectroscopy. - 0003-7028 .- 1943-3530. ; 60:11, s. 1217-1240
  • Tidskriftsartikel (refereegranskat)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, Aobs, and the true absorbance, Atrue. 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., Atrue = f(Aobs). 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.
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11.
  • Bengtsson, Magnus, et al. (författare)
  • Fungus covered insulator materials studied with laser-induced fluorescence and principal component analysis
  • 2005
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 59:8, s. 1037-1041
  • Tidskriftsartikel (refereegranskat)abstract
    • A method combining laser-induced fluorescence and principal component analysis to detect and discriminate between algal and fungal growth on insulator materials has been studied. Eight fungal cultures and four insulator materials have been analyzed. Multivariate classifications were utilized to characterize the insulator material, and fungal growth could readily be distinguished from a clean surface. The results of the principal component analyses make it possible to distinguish between algae infected, fungi infected, and clean silicone rubber materials. The experiments were performed in the laboratory using a fiber-optic fluorosensor that consisted of a nitrogen laser and an optical multi-channel analyzer system.
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12.
  • Bengtsson, Magnus, et al. (författare)
  • Remote laser-induced breakdown spectroscopy for the detection and removal of salt on metal and polymeric surfaces
  • 2006
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 60:10, s. 1188-1191
  • Tidskriftsartikel (refereegranskat)abstract
    • The detection of contamination such as salt in outdoor high-voltage insulator systems and its subsequent removal are vital for a reliable transmission of electric power. Remote detection of salt on a copper metal surface was carried out by using a mobile laser-induced breakdown spectroscopy (LIBS) Lidar system with a laser wavelength of 355 nm. Detection of salt on a polymeric high-voltage insulator was obtained when an additional lens was inserted into the beam path, and the number of photons that was detected could be calculated by using a calibrated white light source. Ablative cleaning could readily be carried out with LIBS and was verified by observing the disappearance of the sodium D-line emission.
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13.
  • Borggren, Jesper, et al. (författare)
  • Spatially Resolved Temperature Measurements Above a Burning Wood Pellet Using Diode Laser-Based Two-Line Atomic Fluorescence
  • 2018
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 72:6, s. 964-970
  • Tidskriftsartikel (refereegranskat)abstract
    • Diode laser-based two-line atomic fluorescence (TLAF) thermometry applied to flames of combusting wood pellets is demonstrated. The temperature above burning wood pellets placed in the hot product gas of gallium seeded laminar flames is measured. The calibration-free technique provides spatially resolved temperatures in one dimension with sufficient temporal resolution to resolve all combustion stages of a pellet, even in highly sooting flames. The temperature above a burning pellet was found to decrease due to the release of volatile gases and the accuracy and precision of the technique is assessed at flame temperatures.
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14.
  • Brackmann, Christian, et al. (författare)
  • Optical and mass spectrometric study of the pyrolysis gas of wood particles
  • 2003
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 57:2, s. 216-222
  • Tidskriftsartikel (refereegranskat)abstract
    • A detailed experimental investigation has been made of the pyrolysis-the first step in biomass combustion-of single birchwood particles. In addition to mass spectrometric and gravimetric analysis, the pyrolysis volatiles were characterized by different optical techniques. Absorption measurements showed a nearly featureless absorption in the ultraviolet spectral region with a continuously stronger absorption for shorter wavelengths. Using different excitation wavelengths, laser-induced fluorescence measurements revealed generally broad spectra in the spectral region from 300-500 nm, which are characteristic spectral signatures for larger hydrocarbons. The optical data were monitored at different times in the pyrolysis process of the particles and compared with the results from the mass spectrometric and gravimetric analysis. The sensitivity of the optical techniques for differentiation between specific molecules was rather low, although formaldehyde could be observed both in absorption and fluorescence spectra. Laser-induced fluorescence measurements were also made for two-dimensional visualization of the pyrolysis volatiles; emitted from heated birchwood particles, indicating much higher flows along the fiber direction than across.
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15.
  • Brackmann, Christian, et al. (författare)
  • Strategies for formaldehyde detection in flames and engines using a single-mode Nd:YAG/OPO laser system
  • 2005
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 59:6, s. 763-768
  • Tidskriftsartikel (refereegranskat)abstract
    • This paper presents technical developments for the detection of formaldehyde (CH2O) using laser-induced fluorescence. The easily accessible third harmonic of the Nd:YAG laser at 355 nm was used for excitation of formaldehyde. In order to investigate potential background fluorescence, e.g., from large molecules such as polyaromatic hydrocarbons, special attention was paid to investigating the possibility of scanning the wavelength of a single-mode Nd: YAG laser under the gain profile, ∼3 cm-1, on and off resonance. Furthermore, a technique for simultaneous detection of formaldehyde and OH using one laser system is presented. The single-mode Nd: YAG laser at 355 nm in combination with an optical parametric oscillator (OPO) laser tuned to 283 nm was used for simultaneous two-dimensional imaging of both species using one charge-coupled device (CCD) detector equipped with a dual filter image separator. The techniques are demonstrated with measurements in laboratory flames and the combined measurements are also demonstrated in an engine.
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16.
  • Brandt, Josef, et al. (författare)
  • High-Throughput Analyses of Microplastic Samples Using Fourier Transform Infrared and Raman Spectrometry
  • 2020
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 74:9, s. 1185-1197
  • Tidskriftsartikel (refereegranskat)abstract
    • Determining microplastics in environmental samples quickly and reliably is a challenging task. With a largely automated combination of optical particle analysis, Fourier transform infrared (FT-IR), and Raman microscopy along with spectral database search, particle sizes, particle size distributions, and the type of polymer including particle color can be determined. We present a self-developed, open-source software package for realizing a particle analysis approach with both Raman and FT-IR microspectroscopy. Our software GEPARD (Gepard Enabled PARticle Detection) allows for acquiring an optical image, then detects particles and uses this information to steer the spectroscopic measurement. This ultimately results in a multitude of possibilities for efficiently reviewing, correcting, and reporting all obtained results.
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17.
  • Brydegaard, Mikkel, et al. (författare)
  • On the Exploitation of Mid-infrared Iridescence of Plumage for Remote Classification of Nocturnal Migrating Birds
  • 2013
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 67:5, s. 477-490
  • Tidskriftsartikel (refereegranskat)abstract
    • A challenging task in ornithology lies in identifying high-altitude nocturnal migrating bird species and genders. While the current approaches including radar, lunar obscuration, and single-band thermal imaging provide means of detection, a more detailed spectral or polarimetric analysis of light has the potential for retrieval of additional information whereby the species and sex could be determined. In this paper, we explore remote classification opportunities provided by iridescent features within feathers in the mid-infrared region. Our approach first involves characterizing the microstructural features of the feather by using rotation and straining, and a scheme for their remote detection is proposed by correlating these microstructural changes to spectral and polarimetric effects. Furthermore, we simulate the spectral signature of the entire bird by using a model that demonstrates how classification would be achieved. Finally, we apply infrared hyperspectral polarization imaging, showing that the net iridescent effect persists for the bird as a whole.
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18.
  • Brydegaard, Mikkel, et al. (författare)
  • Realistic Instrumentation Platform for Active and Passive Optical Remote Sensing.
  • 2016
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 70:2, s. 372-385
  • Tidskriftsartikel (refereegranskat)abstract
    • We describe the development of a novel versatile optical platform for active and passive remote sensing of environmental parameters. Applications include assessment of vegetation status and water quality. The system is also adapted for ecological studies, such as identification of flying insects including agricultural pests. The system is based on two mid-size amateur astronomy telescopes, continuous-wave diode lasers at different wavelengths ranging from violet to the near infrared, and detector facilities including quadrant photodiodes, two-dimensional and line scan charge-coupled device cameras, and a compact digital spectrometer. Application examples include remote Raman-laser-induced fluorescence monitoring of water quality at 120 m distance, and insect identification at kilometer ranges using the recorded wing-beat frequency and its spectrum of overtones. Because of the low cost this developmental platform is very suitable for advanced research projects in developing countries and has, in fact, been multiplied during hands-on workshops and is now being used by a number of groups at African universities.
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19.
  • Cappel, Ute B, et al. (författare)
  • Removing cosmic ray features from Raman map data by a refined nearest neighbor comparison method as a precursor for chemometric analysis.
  • 2010
  • Ingår i: Applied Spectroscopy. - : Sage Publications. - 0003-7028 .- 1943-3530. ; 64:2, s. 195-200
  • Tidskriftsartikel (refereegranskat)abstract
    • An algorithm to remove cosmic ray (CR) features from Raman spectra collected in mapping experiments using a charge-coupled device (CCD) is presented. Each spectrum is compared to spectra collected from adjacent points in space using correlation values. The most similar neighbor (MSN) spectrum is selected, offset, and used for identification of CRs. The offset values are defined in terms of the noise level for data with a low signal-to-noise ratio and in terms of the peak height for data with a high signal-to-noise ratio. Scaled intensity values of the MSN spectra are used for replacement of contaminated pixels, allowing for full recovery of underlying spectral features. The algorithm is applicable for any Raman map where the particle sizes within the analyzed mixture are larger than the sampling size or to any other data where the sampling is more frequent than the variation, e.g., time series or temperature profiles. Its application to several maps of pharmaceutical samples is discussed here. With an appropriate offset value for the MSN spectra, no misdetections occur, and all CRs more intense than the offset are removed, which includes the CRs that would have hampered subsequent chemometric analysis by methods such as principal component analysis (PCA).
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20.
  • Chauchard, F, et al. (författare)
  • MADSTRESS: A linear approach for evaluating scattering and absorption coefficients of samples measured using time-resolved spectroscopy in reflection
  • 2005
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 59:10, s. 1229-1235
  • Tidskriftsartikel (refereegranskat)abstract
    • Time-resolved spectroscopy is a powerful technique permitting the separation of the scattering properties from the chemical absorption properties of a sample. The reduced scattering coefficient and the absorption coefficient are usually obtained by fitting diffusion or Monte Carlo models to the measured data using numerical optimization techniques. However, these methods do not take the spectral dimension of the data into account during the evaluation procedure, but evaluate each wavelength separately. A procedure involving multivariate methods may seem more appealing for people used to handling conventional near-infrared data. In this study we present a new method for processing TRS spectra in order to compute the absorption and reduced scattering coefficients. This approach, MADSTRESS, is based on linear regression and a twodimensional (2D) interpolation procedure. The method has allowed us to calculate absorption and scattering coefficients of apples and fructose powder. The accuracy of the method was good enough to provide the identification of fructose absorption peaks in apple absorption spectra and the construction of a calibration model predicting the sugar content of apples.
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21.
  • Cuss, Chad, et al. (författare)
  • Advanced residuals analysis for determining the number of PARAFAC components in dissolved organic matter
  • 2016
  • Ingår i: Applied Spectroscopy. - Thosand Oaks : Sage Publications. - 0003-7028 .- 1943-3530. ; 70:2, s. 334-346
  • Tidskriftsartikel (refereegranskat)abstract
    • Parallel factor analysis (PARAFAC) has facilitated an explosion in research connecting the fluorescence properties of dissolved organic matter (DOM) to its functions and biogeochemical cycling in natural and engineered systems. However, the validation of robust PARAFAC models using split-half analysis requires an oft unrealistically large number (hundreds to thousands) of excitation–emission matrices (EEMs), and models with too few components may not adequately describe differences between DOM. This study used self-organizing maps (SOM) and comparing changes in residuals with the effects of adding components to estimate the number of PARAFAC components in DOM from two data sets: MS (110 EEMs from nine leaf leachates and headwaters) and LR (64 EEMs from the Lena River). Clustering by SOM demonstrated that peaks clearly persisted in model residuals after validation by split-half analysis. Plotting the changes to residuals was an effective method for visualizing the removal of fluorophore-like fluorescence caused by increasing the number of PARAFAC components. Extracting additional PARAFAC components via residuals analysis increased the proportion of correctly identified size-fractionated leaf leachates from 56.0 ± 0.8 to 75.2 ± 0.9%, and from 51.7 ± 1.4 to 92.9 ± 0.0% for whole leachates. Model overfitting was assessed by considering the correlations between components, and their distributions amongst samples. Advanced residuals analysis improved the ability of PARAFAC to resolve the variation in DOM fluorescence, and presents an enhanced validation approach for assessing the number of components that can be used to supplement the potentially misleading results of split-half analysis.
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22.
  • Doherty, Walter J, et al. (författare)
  • Molecular ordering in monolayers of an alkyl-Substituted perylene-bisimide dye by attenuated total reflectance ultraviolet-visible spectroscopy
  • 2005
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 59:10, s. 1248-1256
  • Tidskriftsartikel (refereegranskat)abstract
    • Surface-relative orientational parameters were determined for monolayer films of N, N'-ditridecylperylenetetracarboxylic dianhydridediimide (C 13-PTCDI) in terms of the relative electronic transition dipole strengths, providing a three-dimensional view of the absorption dipole distribution. In order to obtain a macroscopically ordered film, C 13-PTCDI was deposited by (1) horizontal Langmuir-Blodgett (LB) transfer onto methyl- and phenyl-silanized glass, and (2) vapor deposition onto oriented films of poly(tetrafluoroethylene) (PTFE) on glass. Films of LB-deposited C13-PTCDI were found to be completely Isotropic prior to annealing. After annealing, these films remained isotropic in the plane of the substrate while the out-of-plane anisotropy was significantly enhanced. In contrast, films of C13-PTCDI vapor deposited onto oriented poly(tetrafluoroethylene) (PTFE)-modified substrates yielded films with a high degree of both in- and out-of-plane anisotropy. Atomic force microscopy (AFM) images of both the LB- and vapor-deposited films show substantial differences in film morphology and long-range order. These results demonstrate that molecular orientation in C13-PTCDI films can be controlled by varying substrate surface chemistry and post-deposition processing. © 2005 Society for Applied Spectroscopy.
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23.
  • Ehn, Andreas, et al. (författare)
  • Advanced laser-based techniques for gas-phase diagnostics in combustion and aerospace engineering
  • 2017
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 71:3, s. 341-366
  • Forskningsöversikt (refereegranskat)abstract
    • Gaining information of species, temperature, and velocity distributions in turbulent combustion and high-speed reactive flows is challenging, particularly for conducting measurements without influencing the experimental object itself. The use of optical and spectroscopic techniques, and in particular laser-based diagnostics, has shown outstanding abilities for performing non-intrusive in situ diagnostics. The development of instrumentation, such as robust lasers with high pulse energy, ultra-short pulse duration, and high repetition rate along with digitized cameras exhibiting high sensitivity, large dynamic range, and frame rates on the order of MHz, has opened up for temporally and spatially resolved volumetric measurements of extreme dynamics and complexities. The aim of this article is to present selected important laser-based techniques for gas-phase diagnostics focusing on their applications in combustion and aerospace engineering. Applicable laser-based techniques for investigations of turbulent flows and combustion such as planar laser-induced fluorescence, Raman and Rayleigh scattering, coherent anti-Stokes Raman scattering, laser-induced grating scattering, particle image velocimetry, laser Doppler anemometry, and tomographic imaging are reviewed and described with some background physics. In addition, demands on instrumentation are further discussed to give insight in the possibilities that are offered by laser flow diagnostics.
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24.
  • Elankovan, P., et al. (författare)
  • Technique for obtaining Raman spectra of contact nuclei In Situ
  • 1986
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 40:5, s. 712-714
  • Tidskriftsartikel (refereegranskat)abstract
    • Secondary nucleation, the formation of new crystals due to the prior presence of other growing crystals, is the primary source of new particles in most industrial crystallizers. Of the various types of secondary nucleation possible, contact nucleation, wherein a disturbance of a growing crystal surface results in nuclei, is thought to be the most prevalent.
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25.
  • Eriksson, Ronja, et al. (författare)
  • Investigation of the Spatial Generation of Stimulated Raman Scattering Using Computer Simulation and Experimentation
  • 2022
  • Ingår i: Applied Spectroscopy. - : Sage Publications. - 0003-7028 .- 1943-3530. ; 26:11, s. 1307-1316
  • Tidskriftsartikel (refereegranskat)abstract
    • Stimulated Raman scattering is a phenomenon with potential use in providing real-time molecular information in three-dimensions (3D) of a sample using imaging. For precise imaging, the knowledge about the spatial generation of stimulated Raman scattering is essential. To investigate the spatial behavior in an idealized case, computer simulations and experiments were performed. For the computer simulations, diffraction theory was used for the beam propagation complemented with nonlinear phase modulation describing the interaction between the light and matter. For the experiments, a volume of ethanol was illuminated by an expanded light beam and a plane inside the volume was imaged in transmission. For generating stimulated Raman scattering, a pump beam was focused into this volume and led to a beam dump after passing the volume. The pulse duration of the two beams were 6 ns and the pump beam energy ranged from 1 to 27 mJ. The effect of increasing pump power on the spatial distribution of the Raman gain and the spatial growth of the signal at different interaction lengths between the beam and the sample was investigated. The spatial width of the region where the stimulated Raman scattering signal was generated for experiments and simulation was 0.21 and 0.09 mm, respectively. The experimental and simulation results showed that most of the stimulated Raman scattering is generated close to the pump beam focus and the maximum peak of the Stokes intensity spatially comes shortly after the peak of the pump intensity.
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26.
  • Ferry, Anders, et al. (författare)
  • Curve fitting and deconvolution of instrumental broadening : a simulated annealing approach
  • 1995
  • Ingår i: Applied Spectroscopy. - : Sage Publications. - 0003-7028 .- 1943-3530. ; 49:3, s. 273-278
  • Tidskriftsartikel (refereegranskat)abstract
    • A curve-fitting procedure based on the simulated annealing algorithm has been developed for the analysis of spectral Raman data. By the inclusion of a priori information about the instrumental broadening in the definition of the cost function that is minimized, effects of the finite instrumental resolution are eliminated from the resulting fit. The ability of the method to reproduce original band shapes is tested on synthesized spectra and FT-Raman spectra of diamond recorded at different resolutions with different apodization functions. The procedure yields the global optimum of the fitted parameters and is easily implemented on a personal computer.
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27.
  • Gao, Qiang, et al. (författare)
  • Gas Temperature Measurement Using Differential Optical Absorption Spectroscopy (DOAS)
  • 2018
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 72:7, s. 1014-1020
  • Tidskriftsartikel (refereegranskat)abstract
    • A nonintrusive method for flow gas temperature measurement using differential optical absorption spectroscopy (DOAS) was demonstrated. A temperature-dependent spectra (TDS) originated from the DOAS spectra of sulfur dioxide (SO2) in the wavelength range of 276–310 nm was introduced, and the relationship between the TDS and the temperature was built through experimental calibration process. This relationship is found to be independent of SO2 concentration and can be used for temperature measurements. The experimental results indicated that the precision of the TDS method is < ± 0.3% for SO2 concentrations higher than 150 ppm with the optical path length of 170 mm. For lower concentrations, the precision is estimated to be ± 0.4% at 1 ppm. The relative deviation between the temperature measured by the TDS method and that measured by a thermocouple is within 3% in the temperature range of 298–750 K, and the TDS method has a quicker response to the fast-changing temperature than the thermocouple.
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28.
  • Goodwin, Christopher M., et al. (författare)
  • A Novel Method to Maintain the Sample Position and Pressure in Differentially Pumped Systems Below the Resolution Limit of Optical Microscopy Techniques
  • 2021
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 75:2, s. 137-144
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a new method to maintain constant gas pressure over a sample during in situ measurements. The example shown here is a differentially pumped high-pressure X-ray photoelectron spectroscopy system, but this technique could be applied to many in situ instruments. By using the pressure of the differential stage as a feedback source to change the sample position, a new level of consistency has been achieved. Depending on the absolute value of the sample-to-aperture distance, this technique allows one to maintain the distance within several hundred nanometers, which is below the limit of typical optical microscopy systems. We show that this method is well suited to compensate for thermal drift. Thus, X-ray photoelectron spectroscopy data can be acquired continuously while the sample is heated and maintaining constant pressure over the sample. By implementing a precise manipulator feedback system, pressure variations of less than 5% were reached while the temperature was varied by 400 ℃. The system is also shown to be highly stable under significant changes in gas flow. After changing the flow by a factor of two, the pressure returned to the set value within 60 s.
  •  
29.
  • Grönlund, Rasmus, et al. (författare)
  • Remote imaging laser-induced breakdown spectroscopy and laser-induced fluorescence spectroscopy using nanosecond pulses from a mobile lidar system
  • 2006
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 60:8, s. 853-859
  • Tidskriftsartikel (refereegranskat)abstract
    • A mobile lidar system was used in remote imaging laser-induced breakdown spectroscopy (LIBS) and laser-induced fluorescence (LIF) experiments. Also, computer-controlled remote ablation of a chosen area was demonstrated, relevant to cleaning of cultural heritage items. Nanosecond frequency-tripled Nd:YAG laser pulses at 355 nm were employed in experiments with a stand-off distance of 60 meters using pulse energies of up to 170 mJ. By coaxial transmission and common folding of the transmission and reception optical paths using a large computer-controlled mirror, full elemental imaging capability was achieved on composite targets. Different spectral identification algorithms were compared in producing thematic data based on plasma or fluorescence light.
  •  
30.
  • Haberkorn, M, et al. (författare)
  • Flow-through picoliter dispenser: A new approach for solvent elimination in FT-IR spectroscopy
  • 2002
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 56:7, s. 902-908
  • Tidskriftsartikel (refereegranskat)abstract
    • A new interface for FT-IR analysis of liquid samples on the basis of solvent elimination is presented. The approach is based on a piezoactuated flow-through microdispenser, a device built of two microstructured silicon wafers designed for micro-liquid handling. It could be verified during preliminary studies using a sequential injection (SI) system for automated liquid handling that the flow-through microdispenser as a possible interface for flow system-FT-IR analysis has the capability of meeting the demands of hyphenated miniaturized liquid handling systems (e.g., mu-HPLC, microhigh performance liquid chromatography), as it successfully provides highly stable, reliable and reproducible operating conditions for liquid handling in the picoliter range. Moreover, an increase in sensitivity for FT-IR measurements could be achieved, lowering the mass detection limit of sugars (such as the investigated sucrose) to 53 picograms. As is demonstrated on the example of an HPLC separation of a mixture of glucose and fructose, interfacing LC systems to FT-IR using a piezoactuated flow-through microdispenser is a feasible and promising approach.
  •  
31.
  • Hsu, Li-Jen, et al. (författare)
  • Sodium and Potassium Released from Burning Particles of Brown Coal and Pine Wood in a Laminar Premixed Methane Flame Using Quantitative Laser-Induced Breakdown Spectroscopy
  • 2011
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 65:6, s. 684-691
  • Tidskriftsartikel (refereegranskat)abstract
    • A quantitative point measurement of total sodium ([Na](total)) and potassium ([K](total)) in the plume of a burning particle of Australian Loy Yang brown coal (23 +/- 3 mg) and of pine wood pellets (63 +/- 3 mg) was performed using laser-induced breakdown spectroscopy (LIBS) in a laminar premixed methane flame at equivalence ratios (Phi) of 1.149 and 1.336. Calibration was performed using atomic sodium or potassium generated by evaporation of droplets of sodium sulfite (Na2SO3) or potassium sulfate (K2SO4) solutions seeded into the flame. The calibration compensated for the absorption by atomic alkalis in the seeded flame, which is significant at high concentrations of solution. This allowed quantitative measurements of sodium (Na) and potassium (K) released into the flame during the three phases of combustion, namely devolatilization, char, and ash cooking. The [Na](total) in the plume released from the combustion of pine wood pellets during the devolatilization was found to reach up to 13 ppm. The maximum concentration of total sodium ([Na](total)(max)) and potassium ([K](total)(max)) released during the char phase of burning coal particles for Phi = 1.149 was found to be 9.27 and 5.90 ppm, respectively. The [Na](total)(max) and [K](total)(max) released during the char phase of burning wood particles for Phi = 1.149 was found to be 15.1 and 45.3 ppm, respectively. For the case of Phi = 1.336, the [Na](total)(max) and [K](total)(max) were found to be 13.9 and 6.67 ppm during the char phase from burning coal particles, respectively, and 21.1 and 39.7 ppm, respectively, from burning wood particles. The concentration of alkali species was higher during the ash phase. The limit of detection (LOD) of sodium and potassium with LIBS in the present arrangement was estimated to be 29 and 72 ppb, respectively.
  •  
32.
  • Jakubek, Ryan S., et al. (författare)
  • Calibration of Raman Bandwidths on the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) Deep Ultraviolet Raman and Fluorescence Instrument Aboard the Perseverance Rover
  • 2023
  • Ingår i: Applied Spectroscopy. - : SAGE Publications Inc.. - 0003-7028 .- 1943-3530.
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, we derive a simple method for calibrating Raman bandwidths for the Scanning Habitable Environments with Raman and Luminescence for Organics and Chemicals (SHERLOC) instrument onboard NASA’s Perseverance rover. Raman bandwidths and shapes reported by an instrument contain contributions from both the intrinsic Raman band (IRB) and instrumental artifacts. To directly correlate bandwidth to sample properties and to compare bandwidths across instruments, the IRB width needs to be separated from instrumental effects. Here, we use the ubiquitous bandwidth calibration method of modeling the observed Raman bands as a convolution of a Lorentzian IRB and a Gaussian instrument slit function. Using calibration target data, we calculate that SHERLOC has a slit function width of 34.1 cm–1. With a measure of the instrument slit function, we can deconvolve the IRB from the observed band, providing the width of the Raman band unobscured by instrumental artifact. We present the correlation between observed Raman bandwidth and intrinsic Raman bandwidth in table form for the quick estimation of SHERLOC Raman intrinsic bandwidths. We discuss the limitations of using this model to calibrate Raman bandwidth and derive a quantitative method for calculating the errors associated with the calibration. We demonstrate the utility of this method of bandwidth calibration by examining the intrinsic bandwidths of SHERLOC sulfate spectra and by modeling the SHERLOC spectrum of olivine. 
  •  
33.
  • Jensen, PS, et al. (författare)
  • Influence of temperature on water and aqueous glucose absorption spectra in the near- and mid-infrared regions at physiologically relevant temperatures
  • 2003
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 57:1, s. 28-36
  • Tidskriftsartikel (refereegranskat)abstract
    • Near- and mid-infrared absorption spectra of pure water and aqueous 1.0 g/dL glucose solutions in the wavenumber range 8000-950 cm(-1) were measured in the temperature range 30-42 C in steps of 2 degreesC. Measurements were carried out with an FT-IR spectrometer and a variable pathlength transmission cell controlled within 0.02 degreesC. Pathlengths of 50 mum and 0.4 mm were used in the mid- and near-infrared spectral region, respectively. Difference spectra were used to determine the effect of temperature on the water spectra quantitatively. These spectra were obtained by subtracting the 37 degreesC water spectrum from the spectra measured at other temperatures. The difference spectra reveal that the effect of temperature is highest in the vicinity of the strong absorption bands, with a number of isosbestic points with no temperature dependence and relatively flat plateaus in between. On the basis of these spectra, prospects for and limitations on data analysis for infrared diagnostic methods are discussed. As an example, the absorptive properties of glucose were studied in the same temperature range in order to determine the effect of temperature on the spectral shape of glucose. The change in water absorption associated with the addition of glucose has also been studied. An estimate of these effects is given and is related to the expected level of infrared signals from glucose in humans.
  •  
34.
  • Johansson, J, et al. (författare)
  • Time-resolved NIR/Vis spectroscopy for analysis of solids: Pharmaceutical tablets
  • 2002
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 56:6, s. 725-731
  • Tidskriftsartikel (refereegranskat)abstract
    • Time-resolved spectroscopy in the visible and near-infrared (NIR) regions was used in a feasibility study for analysis of solid pharmaceuticals. The objective of the experiments was to study the interaction of light with pharmaceutical solids and to investigate the usefulness of the method as an analytical toot for spectroscopic analysis. In these experiments, a pulsed Ti:sapphire laser and white light generation in water was utilized to form a pulsed light source in the visible/NIR region. The light was focused onto the surface of tablets, and the transmitted light was detected by a time-resolving streak camera. Two types of measurements were performed. First, a spectrometer was put in front of the streak camera for spectral resolution. Secondly, the signal originating from different locations of the sample was collected. Time-resolved and wavelength/spatially resolved data were generated and compared for a number of different samples. The most striking result from the experiments is that the typical optical path length through a 3.5-mm-thick tablet is about 20-25 cm. This indicates very strong multiple scattering in these samples. Monte Carlo simulations and comparison with experimental data support very high scattering coefficients on the order of 500 cm(-1). Furthermore, the data evaluation shows that photons with a particular propagation time through the sample contain a higher chemical contrast than other propagation times or than steady-state information. In conclusion, time-resolved NIR spectroscopy yields more information about solid pharmaceutical samples than conventional steady-state spectroscopy.
  •  
35.
  • Johansson, Olof, et al. (författare)
  • Detection of hydrogen peroxide using photofragmentation laser-induced fluorescence.
  • 2008
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 62:1, s. 66-72
  • Tidskriftsartikel (refereegranskat)abstract
    • Photofragmentation laser-induced fluorescence (PF-LIF) is for the first time demonstrated to be a practical diagnostic tool for detection of hydrogen peroxide. Point measurements as well as two-dimensional (2D) measurements in free-flows, with nitrogen as bath gas, are reported. The present application of the PF-LIF technique involves one laser, emitting radiation of 266 nm wavelength, to dissociate hydrogen peroxide molecules into OH radicals, and another laser, emitting at 282.25 nm, to electronically excite OH, whose laser-induced fluorescence is detected. The measurement procedure is explained in detail and a suitable time separation between photolysis and excitation pulse is proposed to be on the order of a few hundred nanoseconds. With a separation time in that regime, recorded OH excitation scans were found to be thermal and the signal was close to maximum. The PF-LIF signal strength was shown to follow the same trend as the vapor pressure corresponding to the hydrogen peroxide liquid concentration. Thus, the PF-LIF signal appeared to increase linearly with hydrogen peroxide vapor-phase concentration. For 2D single shot measurements, a conservatively estimated value of the detection limit is 30 ppm. Experiments verified that for averaged point measurements the detection limit was well below 30 ppm.
  •  
36.
  • Johansson, Ursula, et al. (författare)
  • Raman spectroscopy of the kaolinite hydroxyls at 77 K
  • 1998
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 52:10, s. 1277-1282
  • Tidskriftsartikel (refereegranskat)abstract
    • Raman spectroscopy of two types of kaolinites has been obtained at liquid nitrogen temperature (77 K) with the use of a Raman microprobe and a thermal stage. The Raman spectrum is characterized by the combination of the frequencies of the inner hydroxyl and the inner surface hydroxyl groups. The inner hydroxyl frequency is reduced, and the outer hydroxyl frequencies move to higher frequencies upon cooling to 77 K. The inner hydroxyl frequency shifts from 3620 cm-1 at 298 K to 3615 cm-1 at 77 K. The two in-phase inner surface hydroxyl frequencies move from 3684 and 3689 cm-1 at 298 K to 3690 and 3699 cm-1 at 77 K. The two out-of-phase vibrations shift from 3650 and 3668 cm-1 to 3656 and 3675 cm-1. The bandwidth of the inner hydroxyl frequency decreases from 3.7 to 2.1 cm-1 at 77 K. The bandwidth of the inner surface hydroxyl frequency (upsilon 1) increases upon cooling from 17.4 to 19.2 cm-1. It is proposed that the increased resolution at low temperature enabled an additional inner surface hydroxyl frequency to be observed.
  •  
37.
  • Kamran, Faisal, et al. (författare)
  • Transmission Near-Infrared (NIR) and Photon Time-of-Flight (PTOF) Spectroscopy in a Comparative Analysis of Pharmaceuticals
  • 2015
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 69:3, s. 389-397
  • Tidskriftsartikel (refereegranskat)abstract
    • We present a comprehensive study of the application of photon time-of-flight spectroscopy (PTOFS) in the wavelength range 1050 1350 nm as a spectroscopic technique for the evaluation of the chemical composition and structural properties of pharmaceutical tablets. PTOFS is compared to transmission near-infrared spectroscopy (NIRS). In contrast to transmission NIRS, PTOFS is capable of directly and independently determining the absorption and reduced scattering coefficients of the medium. Chemometric models were built on the evaluated absorption spectra for predicting tablet drug concentration. Results are compared to corresponding predictions built on transmission NIRS measurements. The predictive ability of PTOFS and transmission NIRS is comparable when models are based on uniformly distributed tablet sets. For non-uniform distribution of tablets based on particle sizes, the prediction ability of PTOFS is better than that of transmission NIRS. Analysis of reduced scattering spectra shows that PTOFS is able to characterize tablet microstructure and manufacturing process parameters. In contrast to the chemometric pseudovariables provided by transmission NIRS, PTOFS provides physically meaningful quantities such as scattering strength and slope of particle size. The ability of PTOFS to quantify the reduced scattering spectra, together with its robustness in predicting drug content, makes it suitable for such evaluations in the pharmaceutical industry.
  •  
38.
  • Kiefer, Johannes, et al. (författare)
  • Laser-Induced Fluorescence Detection of Hot Molecular Oxygen in Flames Using an Alexandrite Laser
  • 2014
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 68:11, s. 1266-1273
  • Tidskriftsartikel (refereegranskat)abstract
    • The use of an alexandrite laser for laser-induced fluorescence (LIF) spectroscopy and imaging of molecular oxygen in thermally excited vibrational states is demonstrated. The laser radiation after the third harmonic generation was used to excite the B-X (0-7) band at 257 nm in the Schumann-Runge system of oxygen. LIF emission was detected between 270 and 380 nm, revealing distinct bands of the transitions from B(0) to highly excited vibrational states in the electronic ground state, X (v > 7). At higher spectral resolution, these bands reveal the common P- and R-branch line splitting. Eventually, the proposed LIF approach was used for single-shot imaging of the two-dimensional distribution of hot oxygen molecules in flames.
  •  
39.
  • Kiefer, Johannes, et al. (författare)
  • Misalignment Effects in Laser-Induced Grating Experiments
  • 2016
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 70:12, s. 2025-2028
  • Tidskriftsartikel (refereegranskat)abstract
    • Laser-induced grating spectroscopy (LIGS) is an experimental method in which two pulsed laser beams and a continuous-wave laser beam have to be superimposed under well-defined angles to generate a coherent signal beam. In this Note, the possible effects of different forms of misalignment are examined. This includes the overlap of the pump lasers as well as the influence of the probe laser alignment on the temporal profile of the signal.
  •  
40.
  • Kröll, Stefan, et al. (författare)
  • Background-free Species Detection In Sooty Flames Using Degenerate 4-wave-mixing
  • 1993
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 47:10, s. 1620-1622
  • Tidskriftsartikel (refereegranskat)abstract
    • The background radiation disturbance in luminous environments has been compared for degenerate four-wave mixing (DFWM) and laser-induced fluorescence (LIF) for OH radical detection in a sooty propane/oxygen flame. The LIF signal generally was considerably stronger than the DFWM signal, but in strongly sooty environments the LIF signal was accompanied by a significant background signal, while the DFWM signal was background-free under all soot loads tested.
  •  
41.
  • Larsson, Kajsa, et al. (författare)
  • Simultaneous Visualization of Hydrogen Peroxide and Water Concentrations Using Photofragmentation Laser-Induced Fluorescence
  • 2017
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 71:9, s. 2118-2127
  • Tidskriftsartikel (refereegranskat)abstract
    • A concept based on photofragmentation laser-induced fluorescence (PFLIF) is for the first time demonstrated for simultaneous detection of hydrogen peroxide (H2O2) and water (H2O) vapor in various mixtures containing the two constituents in a bath of argon gas. A photolysis laser pulse at 248 nm dissociates H2O2 into OH fragments, whereupon a probe pulse, delayed 100 ns and tuned to an absorption line in the A2Σ+ (v = 1) ← X2Π(v = 0) band of OH near 282 nm, induces fluorescence. The total OH fluorescence reflects the H2O2 concentration, while its spectral shape is utilized to determine the H2O concentration via a model predicting the ratio between the fluorescence intensities of the A2Σ+ (v = 1) → X2Π(v = 1) and the A2Σ+ (v = 0) → X2Π(v = 0) bands. The H2O detection scheme requires that the bath gas has a collisional cross-section with OH(A) that is significantly lower than that of H2O, which is the case for argon. Spectrally dispersed OH fluorescence spectra were recorded for five different H2O2/H2O/Ar mixtures; the H2O2 concentration in the range of 30–500 ppm and the H2O concentration in the range of 0–3%. Fluorescence intensity ratios predicted by the model for these mixtures agree very well with corresponding experimental data, which thus validates the model. The concept was also demonstrated for two-dimensional imaging, using two intensified charge-coupled device (CCD) cameras for signal detection. Water content was here sensed through the different temporal characteristics of the two fluorescence bands by triggering the two cameras so that one captures the total OH fluorescence while the other one captures only the early part, which mainly stems from A2Σ+ (v = 1) → X2Π(v = 1) fluorescence. Hence, the H2O2 concentration is reflected by the image of the camera recording the total OH fluorescence, whereas H2O concentration is extracted from the ratio between the two camera images. Quantification of the concentrations was carried out based on calibration measurements performed in known mixtures of H2O2 (30–500 ppm) and H2O (0–3%) in bulk argon. The detection limits for single-shot imaging are estimated to be 20 ppm for H2O2 and 0.05% for H2O. The authors believe that the concept provides a valuable asset in, for example, pharmaceutical or aseptic food packaging applications, where H2O2/H2O vapor is routinely used for sterilization.
  •  
42.
  • Larsson, Kajsa, et al. (författare)
  • Simultaneous Visualization of Water and Hydrogen Peroxide Vapor Using Two-Photon Laser-Induced Fluorescence and Photofragmentation Laser-Induced Fluorescence
  • 2014
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 68:12, s. 1333-1341
  • Tidskriftsartikel (refereegranskat)abstract
    • A concept based on a combination of photofragmentation laser-induced fluorescence (PF-LIF) and two-photon laser-induced fluorescence (LIF) is for the first time demonstrated for simultaneous detection of hydrogen peroxide (H2O2) and water (H2O) vapor. Water detection is based on two-photon excitation by an injection-locked krypton fluoride (KrF) excimer laser (248.28 nm), which induces broadband fluorescence (400-500 nm) from water. The same laser simultaneously photodissociates H2O2, whereupon the generated OH fragments are probed by LIF after a time delay of typically 50 ns, by a frequency-doubled dye laser (281.91 nm). Experiments in six different H2O2/H2O mixtures of known compositions show that both signals are linearly dependent on respective species concentration. For the H2O2 detection there is a minor interfering signal contribution from OH fragments created by two-photon photodissociation of H2O. Since the PF-LIF signal yield from H2O2 is found to be at least similar to 24 000 times higher than the PF-LIF signal yield from H2O at room temperature, this interference is negligible for most H2O/H2O2 mixtures of practical interest. Simultaneous single-shot imaging of both species was demonstrated in a slightly turbulent flow. For single-shot imaging the minimum detectable H2O2 and H2O concentration is 10 ppm and 0.5%, respectively. The proposed measurement concept could be a valuable asset in several areas, for example, in atmospheric and combustion science and research on vapor-phase H2O2 sterilization in the pharmaceutical and aseptic food-packaging industries.
  •  
43.
  • Leffler, Tomas, et al. (författare)
  • Laser-Induced Photofragmentation Fluorescence Imaging of Alkali Compounds in Flames
  • 2017
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 71:6, s. 1289-1299
  • Tidskriftsartikel (refereegranskat)abstract
    • Laser-induced photofragmentation fluorescence has been investigated for the imaging of alkali compounds in premixed laminar methane–air flames. An ArF excimer laser, providing pulses of wavelength 193 nm, was used to photodissociate KCl, KOH, and NaCl molecules in the post-flame region and fluorescence from the excited atomic alkali fragment was detected. Fluorescence emission spectra showed distinct lines of the alkali atoms allowing for efficient background filtering. Temperature data from Rayleigh scattering measurements together with simulations of potassium chemistry presented in literature allowed for conclusions on the relative contributions of potassium species KOH and KCl to the detected signal. Experimental approaches for separate measurements of these components are discussed. Signal power dependence and calculated fractions of dissociated molecules indicate the saturation of the photolysis process, independent on absorption cross-section, under the experimental conditions. Quantitative KCl concentrations up to 30 parts per million (ppm) were evaluated from the fluorescence data and showed good agreement with results from ultraviolet absorption measurements. Detection limits for KCl photofragmentation fluorescence imaging of 0.5 and 1.0 ppm were determined for averaged and single-shot data, respectively. Moreover, simultaneous imaging of KCl and NaCl was demonstrated using a stereoscope with filters. The results indicate that the photofragmentation method can be employed for detailed studies of alkali chemistry in laboratory flames for validation of chemical kinetic mechanisms crucial for efficient biomass fuel utilization.
  •  
44.
  • Li, Bo, et al. (författare)
  • Methyl Radical Imaging in Methane-Air Flames Using Laser Photofragmentation-Induced Fluorescence
  • 2015
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 69:10, s. 1152-1156
  • Tidskriftsartikel (refereegranskat)abstract
    • Imaging detection of methyl radicals has been performed in laminar premixed methane-air flames at atmospheric pressure. A nanosecond Q-switched neodymium-doped yttrium aluminum garnet (Nd : YAG) laser was employed to provide the fifth-harmonic-generated 212.8 nm laser beam. The intense ultraviolet (UV) laser pulse was sent through the flame front to photodissociate The methyl (CH3) radicals in the reaction zone of the flames stabilized on a piloted jet flame burner. The emission spectra from the photodissociated fragments were collected using an imaging spectrometer with the flame-front structure spatially resolved. Combining the spatial and spectral information, we recognized that the emission from the (A-X) methine (CH) transitions located at 431 nm was generated from the CH3 photolysis and could be used to visualize the distribution of CH3 radicals. With proper filtering, the high-power UV laser (around 15 mJ/pulse) provided by the compact Nd : YAG laser makes it possible to visualize CH3 distribution naturally generated in the reaction zone of laminar methane-air premixed flames.
  •  
45.
  • Li, Tianqi, et al. (författare)
  • Application of Tunable Diode Laser Spectroscopy for the Assessment of Food Quality
  • 2017
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 71:5, s. 929-938
  • Tidskriftsartikel (refereegranskat)abstract
    • Adequate food packaging is important to ensure food quality and prolong the shelf life of food. Frequently, the method of modified atmosphere packaging (MAP) is used. We used a tunable diode laser spectroscopy technique to detect the oxygen content in food packages, e.g., in packaged milk and bread. Different detection geometries were adopted to be able to collect scattering light that had passed through the gas volume in the packages, and to avoid the disturbance of ambient air. Furthermore, studies of the bread-baking process have been performed by measuring the water vapor signals in a fermenting dough. The results demonstrate that the technique has a great potential for nonintrusive assessment of food quality and the bread-baking process.
  •  
46.
  • Li, TQ (författare)
  • H-2 NMR spectra for D2O adsorbed on oriented cellulose fibers
  • 1996
  • Ingår i: APPLIED SPECTROSCOPY. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 50:12, s. 1512-1518
  • Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
    • 2H NMR spectra for D2O adsorbed on cellulose fibers which are macroscopically oriented demonstrate that the axis of cellulose fibers can be regarded as the director of the average molecular motion of the adsorbed D2O. The spectra for samples prepared from fiber sheets depend on the orientation of the sheets with respect to the magnetic field as well as the fiber orientation in the sheets. When the sheets are oriented perpendicular to the magnetic field, all the fibers in the sheets are perpendicular to the field irrespective of the fiber orientations in the sheets, and a partially overlapped quadrupole splitting is observed. When the sheets are oriented parallel to the magnetic field, the observed spectra deviate significantly from the expected 2D powder patterns, and the distribution of fiber orientations in the sheets has a significant influence on the observed band shape. An N-site mutual exchange model was used to account for the lateral diffusion of water molecules from one fiber to another. In a comparison of the simulated spectra based on the N-site mutual exchange model with the experimentally recorded spectra, the average lifetime for the adsorbed D2O molecules to reside on cellulose fibrils was estimated to be about 1.5 ms.
  •  
47.
  • Li, Zheming, et al. (författare)
  • Simultaneous Burst Imaging of Dual Species Using Planar Laser-Induced Fluorescence at 50 kHz in Turbulent Premixed Flames
  • 2017
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 71:6, s. 1363-1367
  • Tidskriftsartikel (refereegranskat)abstract
    • Spatially and temporally resolved measurements are of great importance in turbulent premixed flame studies, especially when investigating rapid processes such as when flame local extinction, re-ignition, or flashback occur in a reacting flow. Here, an experimental approach for simultaneously probing two different species at high frame rates (50 kHz) is presented by employing a multi-YAG laser system. The laser radiation at 355 nm generated by a multi-YAG laser system was split into two beam paths: one beam for exciting formaldehyde and the other for pumping an optical parametric oscillator (OPO). To be able to capture the resulting fluorescence at such a high frame rate without significant loss in spatial resolution, two framing cameras, containing a total of 16 intensified charge-coupled devices (CCDs), were employed. In principle, the proposed setup provides the possibility of probing formaldehyde and simultaneously accessing the distribution of one other relevant species at this high frame rate. In this demonstration, the laser wavelength was tuned to 283 nm and, in conjunction with the 355 nm beam path, simultaneously high speed two-dimensional (2D) visualization of OH-radicals and formaldehyde was achieved. A modified flat flame, McKenna-type burner was used to provide a turbulent premixed jet-flame supported by a surrounding pilot flame. Local flame extinction and re-ignition processes were recorded for fuel/air jet speeds of 120 m/s.
  •  
48.
  • McMahon, Paula M., et al. (författare)
  • A constant-temperature Raman cell for the study of supersaturated aqueous solutions
  • 1986
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 0003-7028 .- 1943-3530. ; 40:2, s. 282-283
  • Tidskriftsartikel (refereegranskat)abstract
    • In order that the phenomena of crystal nucleation and growth from solution can be fully understood, the current knowledge of supersaturated solution structure must be extended. Previous studies on Raman spectroscopy of aqueous metal nitrate solutions indicated the presence of solvated ions, solvent separated ion pairs, contact ion pairs, and ion agglomerates as a function of concentration. Unfortunately, the concentration range of these studies did not include supersaturated solutions. It is the purpose of this work to describe an experimental technique which allows the study of supersaturated solutions.
  •  
49.
  • Miles, Paul C., et al. (författare)
  • Atmospheric Pressure Acetylene Detection by UV Photo-Fragmentation and Induced C-2 Emission
  • 2013
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 67:1, s. 66-72
  • Tidskriftsartikel (refereegranskat)abstract
    • Detection of C2H2 via UV photo-fragmentation, followed by monitoring the C(2)d(3)Pi(g)-a(3)Pi(u) fluorescence, is explored at atmospheric pressure and at temperatures of 295 K, 600 K, and 800 K, for excitation wavelengths 210 to 240 am using a broadband laser source (similar to 3 cm(-1) fwhm). At the lower temperature, C-2 emissions correlate closely with C2H2 (A) over tilde <- X absorption bands, and the excitation spectra suggest a higher-transition probability for the v(4)'' = 2 and 3 states than for the v(4)'' = 0 and 1 states. As temperature increases, the excitation spectra exhibit a higher nonresonant background.
  •  
50.
  • Murphy, Kathleen, 1972 (författare)
  • A note on determining the extent of the water Raman peak in fluorescence spectroscopy
  • 2011
  • Ingår i: Applied Spectroscopy. - : SAGE Publications. - 1943-3530 .- 0003-7028. ; 65:2, s. 233-236
  • Tidskriftsartikel (refereegranskat)abstract
    • A method is proposed for automatically determining the upper and lower boundaries of the Raman scatter peak in fluorescence spectroscopy from empirical data. Accurate peak boundaries are needed to calculate accurate Raman peak areas, used for normalizing fluorescence signals to produce data in units that are comparable between instruments. Comparisons of Raman peak boundaries across nine individual instruments (FluoroMax 3 (FM3) fluorometers from HORIBA Jobin Yvon and Cary Eclipse (CE) fluorometers from Varian Inc.) at the excitation wavelength λex = 350 nm reveal consistent results. At 350 nm excitation, the Raman peak was confined by the emission wavelengths of 382-418 nm, with boundaries determined for the FM3 fluorometers deviating by no more than 0.5 nm and 1.5 nm with respect to the start and end of the peak, and CE fluorometers deviating by up to 1.5 nm and 2 nm, respectively. Peak width was a function of fluorometer type and excitation wavelength. For the FM3 instruments, widths increased from approximately 30 nm at λex = 300 nm to 40 nm at λex = 380 nm, while for the CE instruments, peaks were approximately 5-8 nm narrower. Code for implementing the procedure in MATLAB, which allows for the adjustment of input parameters to compensate for noisy data, is provided in the Supplemental Material (available online). © 2011 Society for Applied Spectroscopy.
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