The presented work reports on an improved analysis of chlorides in cement and concrete using molecular LIBS. The quantitative determination of the atomic chlorine emission requires sophisticated ...setups under helium atmosphere and specialized spectrometers. Molecular LIBS can be performed with standard spectrometers and without additional buffer gas. In a LIBS plasma of chloride contaminated cement or concrete atomic chlorine and calcium form calcium-mono-chloride (CaCl) radicals which will be used for the quantification of chlorides. By calculating the intensity ratio of chlorine dependent and independent molecular band emission the standard deviation of the intensity ratio compared to the absolute species emission can be reduced by a factor of 5. Air purging further reduces the total standard deviation by two-thirds compared to measurements in ambient air without purging. A linear calibration with a limit of detection and limit of quantification complying with the threshold of a critical chloride contamination in concrete is determined. Spatially and temporally resolved measurements of different fixed concentrations of chloride are shown to proof the homogeneity of reference samples. In order to determine the diffusion process of the chloride contamination measurements on a drilling core are presented. As supplemental method for micro analysis, spatially resolved energy dispersive X-ray (EDX) measurements are performed. EDX can help to reveal the atomic distribution in a hydrated sample on a scale much smaller than the spot size of the laser. Thereby, relevant reaction partners for the molecular formation could be identified.
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•New, easy-to-use processing of molecular spectra in LIBS plasma improves elemental quantification of chlorides in concrete•Application in civil engineering with cost-efficient detectors•LOD improvement by a factor of 5 in compliance with the threshold given in DIN EN 206:2017‐01 for concrete structures•Time resolved molecular mapping for detecting chloride diffusion processes in concrete drilling cores
Due to the penetration of harmful chlorides into concrete, e.g. from de-icing salt, damage processes such as chloride-related pitting corrosion can occur if critical values are exceeded. In this ...study, multiphase materials such as chloride-contaminated concrete are examined in detail. A direct comparison is made by analyzing the spectroscopic information of simultaneously measured atomic and molecular emissions with laser-induced breakdown spectroscopy (LIBS). In addition, the influence on the calibration is examined on the basis of the combined spectral information of both reaction paths of the penetrated chlorides. The calibration models of univariate and multivariate methods were validated using reference samples with wet chemical analysis. The results are applied to a concrete sample of a parking deck, which was also analyzed by potentiometric wet chemistry. In order to account for the heterogeneity of concrete, spatially (200 μm) and spectroscopically (0.1 nm) resolved LIBS measurements were performed using a fully automated laboratory system. Simultaneous measurements with three spectrometers allow the analysis of the emission processes of several elements such as Cl, Ca, O, Si and Mg as well as the newly formed molecules CaO and CaCl. The evaluation of the molecular emission in combination with atomic lines extends the analytical performance, since different concrete phases such as aggregates and cement matrix can be better represented. The measurements were carried out in ambient air and with helium purge gas. The limit of detection (LOD) achieved for a combined evaluation of atomic and molecular emission was determined to be 0.028 wt%.
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•Simultaneous measurement of atomic and molecular LIBS spectra for a direct comparison of the chloride determination method.•Multivariate combination of atomic and molecular spectra for improved quantification of chlorides in concrete analysis.•Matrix phase separation of heterogeneous samples by using atomic and molecular spectral information.•Mapping and determination of the chloride ingress in concrete analysis by combined atomic and molecular spectral information.
A comparative study of residual thermal effects in aluminum following ns- and fs-laser ablation shows a surprisingly similar trend in their behavior, despite many differences between ns and fs ...laser-matter interactions. At laser fluences above the ablation threshold where plasmas are produced and at a sufficiently high ambient gas pressure, an enhanced coupling of pulsed laser energy to the sample occurs. This effect appears to be a universal phenomenon for both ns- and fs-laser ablation in gas media. Furthermore, in contrast to the common belief that residual thermal energy is negligible in fs-laser ablation, our study shows that up to 70% of the incident pulse energy can be retained in the sample following single-pulse fs-laserablation in 1-atm air. In both ns- and fs-laser ablation, the major factors governing thermal energy coupling to the sample are the laser fluence and ambient gas pressure. Residual thermal energy deposition decreases with reducing ambient gas pressure.
The operating current of a semiconductor laser optically locked to a high-finesse reference cavity can be controlled using a second-harmonic lock-in technique. The authors present theoretical ...calculations for this novel servo scheme. For stabilization and noise reduction of semiconductor lasers, the optical lock to a high-finesse cavity with a feedback phase servo has become a standard technique. An additional servo for the laser current is desirable for combining good tuning capability and high spectral purity. It is demonstrated that such a servo can easily be established with no changes in the optical setup. The practical applicability of this technique has been demonstrated in a setup with a 780-mm laser diode.< >
Measurement of polarization and applications Kohns, P.; Machekhin, Y.
Proceedings of LFNM 2002. 4th International Workshop on Laser and Fiber-Optical Networks Modeling (IEEE Cat. No.02EX549),
2002
Conference Proceeding
We present a polarization measuring system which is capable to determine the complete, Stokes vector of radiation with a wavelength from deep ultraviolet (i.e. 190 nm) to the visible spectral range. ...Due to a special design the entire wavelength range is covered by one single device (i.e. no exchange of optical components is necessary). In addition the system is able to determine the Jones and the Mueller matrices of lenses, waveplates and other samples automatically and spatially resolved within the same wavelength region. The system consists of a polarization state generator and a polarization sensitive detector consisting of a rotating waveplate, a polarizer, and a detector. A fast Fourier algorithm provides the four Stokes parameters of the light where all parameters are calculated independently. By tuning the polarization of the illuminating light we calculate the Jones matrix and the birefringence of the sample. Under industrial conditions we found an accuracy of the stress birefringence of 0.1 nm and an accuracy of the azimuth of the fast axis of 0.1/spl deg/. Because polarization is a very important property of radiation, the system has a lot of applications. Examples are the testing of optical elements like waveplates, polarizers and lens system.
Measuring methods of the polarization state of the intense and wide-aperture laser radiation with three profile biometric gratings are grounded. Knowledge of the dependence of the bolometer ...transformation coefficient on effective linear incident radiation intensity allows to determine coefficient of non-uniformity of incident radiation intensity distribution across entire gratings aperture, polarize coefficients of radiation interaction with bolometers, and straight radiation intensity from the signals of each bolometric elements via step-by-step approximation. Values of normalized transformation coefficients of each grating and linearized signals of gratings are determined with obtained radiation parameters. The linearized signals of gratings give us the possibility to consider three methods of determination of parameters of linear polarization of radiation in optic beam cross-section, and also parameters of elliptic polarization of radiation: relative semi-axes of ellipse, their angle directions in beam cross-section, and cosine of lagging angle between electric components of electromagnetic radiation. The dominant systematic errors at the expense of nonlinearity of bolometer transformation characteristic are eliminated in grounded methods. Errors of measured parameters of laser radiation state are analyzed.
Three bolometric gratings have to be used for measurements of the polarization state of the laser radiation. It is possible to eliminate systematic errors of such measurements caused by the ...nonlinearity of the bolometer transformation characteristic if beforehand eliminate the similar errors from grating signals. This work concerns the development of measuring method of energy parameters of the laser radiation, the coefficient of non-uniformity of the radiation intensity distribution, and the polarize coefficients of bolometer interaction with the radiation, and also technique of elimination of systematic errors at the expense of the bolometer nonlinearity from the obtained results. The aim of the work achieves with the usage of known cubic dependence of the bolometer transformation coefficient on the incident on the bolometer linear radiation intensity, obtained dependencies of coefficient of non-uniformity of radiation intensity distribution across entire gratings aperture, and polarize coefficients of interaction. Energy parameters of radiation are solved with cubic measuring equation with step-by-step correction of the coefficient of non-uniformity distribution; the polarize coefficients of the interaction; and incident linear radiation intensity. The analysis of the obtained measurement results are carried out.
This research shows the changes of the absorption ability of the surface of tantalum foil when it is heated by means of continuous-wave CO/sub 2/ laser in the air at temperature 600/spl deg/C - ...650/spl deg/C. The absorption ability of the sample (when it was completely cooled down after the laser heating) is evaluated by measuring the slope angle of the foil surface temperature growth under the testing laser beam. This study also performed experiments where the heating of one sample is interrupted at definite period of time and the magnitude of absorption capacity is measured. The measurement of Wickers microhardness in surface districts which had undergone laser heating is also conducted.
