B. M. Suri

Analysis of trace elements in complex matrices (soil) by Laser Induced Breakdown Spectroscopy (LIBS)

Direct spectro-chemical analysis of trace elements in complex matrices like minerals and soil is usually difficult because of possible interference from the intense background spectrum of the major components generated in the plasma. Optimization of the Laser Induced Breakdown Spectroscopy (LIBS) technique is essential for routine analysis of such samples. In the present work, we have shown that low detection limits can be achieved for trace elements like copper, zinc, and calcium in soil samples by using high resolution echelle spectrographs coupled to the LIBS system, and eliminating the background by subtraction of a suitable matrix “blank” spectrum. It is also shown that the LOD (limits of detection) can be further reduced by suitable data processing techniques like signal addition from multiple lines provided by the wide-range echelle system and use of correlation function calculation with a pure element spectrum. The validity of our LIBS technique was confirmed by conventional Atomic Absorption Spectroscopy (AAS) analysis for the same analyte after pre-concentration.

Optimized LIBS setup with echelle spectrograph-ICCD system for multi-elemental analysis

Laser-Induced Breakdown Spectroscopy (LIBS) is well recognized as a promising tool for in situ/remote elemental analysis of environmental, archeological, clinical, and hazardous samples. With the aim of quantifying trace elements in such samples, using LIBS technique, an echelle spectrograph-ICCD system with high sensitivity and good resolution has been assembled. Various important parameters of this system were studied and optimized. Conditions for getting good quality LIBS spectra and signal for multielemental analysis have been achieved, and these are discussed and illustrated in this paper.

Quantitative elemental analysis of steel using calibration-free laser-induced breakdown spectroscopy

We report the quantitative elemental analysis of a steel sample using calibration-free laser-induced breakdown spectroscopy (CF-LIBS). A Q-switched Nd:YAG laser (532 nm wavelength) is used to produce a plasma by focusing it onto a steel sample in air at atmospheric pressure. The time-resolved spectra from atomic and ionic emission lines of the steel elements are recorded by an echelle grating spectrograph coupled with a gated intensified CCD camera and are used for the plasma characterization and quantitative analysis of the sample. The time delay at which the plasma is in local thermodynamic equilibrium as well as optically thin, necessary for elemental analysis, is deduced. An algorithm for the CF-LIBS relating the experimentally measured spectral intensity values with the basic physics of the plasma is developed and used for the determination of Fe, Cr, Ni, Mg, and Si concentrations in the steel sample. The analytical results obtained from the CF-LIBS technique agree well with the certified values of the elements in the sample, with relative uncertainties of less than 5%.

High-lying even-parity excited levels of atomic samarium

We report the observation of new high-lying even-parity excited levels of samarium in the energy region 34 814.4 cm^-1 to 35 110.9 cm^-1. These levels are identified with two-color laser-induced fluorescence spectroscopy in an atomic beam. The values of the total angular momentum (J) of these levels are assigned. Our results are compared with the results obtained with two-color, three-photon photoionization spectroscopy in the same energy region reported earlier in the literature [J. Opt. Soc. Am. B13, 641 (1996)]. The similarities and differences observed in the spectra by two techniques have been discussed, reaffirming the complementary nature of the two techniques for laser spectroscopy of highly excited levels.

Study of even-parity autoionization resonances of atomic uranium by three-color optogalvanic spectroscopy

We report our investigation on the even-parity autoionization (AI) resonances of atomic uranium in the energy region 52,850–53,350  cm−1, using the three-color optogalvanic spectroscopy technique in a U–Ne hollow cathode discharge lamp with three pulsed dye lasers. To the best of our knowledge, this is the first report of observation of even-parity AI states in atomic uranium lying more than 2000  cm−1 above the ionization limit. We have used four different excitation schemes, starting from the lowest metastable state of uranium at 620  cm−1 (K505). We have identified 102 new even-parity AI resonances in atomic uranium and assigned probable total angular momentum (J) values to these resonances. By observing 25 out of these 102 AI resonances through more than one excitation pathway, the ambiguity in the assignment of their J values has been reduced considerably.

Homogeneity testing and quantitative analysis of manganese (Mn) in vitrified Mn-doped glasses by laser-induced breakdown spectroscopy (LIBS)

Laser-induced breakdown spectroscopy (LIBS), an atomic emission spectroscopy method, has rapidly grown as one of the best elemental analysis techniques over the past two decades. Homogeneity testing and quantitative analysis of manganese (Mn) in manganese-doped glasses have been carried out using an optimized LIBS system employing a nanosecond ultraviolet Nd:YAG laser as the source of excitation. The glass samples have been prepared using conventional vitrification methods. The laser pulse irradiance on the surface of the glass samples placed in air at atmospheric pressure was about 1.7×109 W/cm2. The spatially integrated plasma emission was collected and imaged on to the spectrograph slit using an optical-fiber-based collection system. Homogeneity was checked by recording LIBS spectra from different sites on the sample surface and analyzing the elemental emission intensities for concentration determination. Validation of the observed LIBS results was done by comparison with scanning electron microscope- ...

Comparison of 138 La: 139 La-isotope-ratio-enhancement calculations by use of spectral-simulation and density-matrix methods

The isotope-ratio-enhancement calculations for 138La are carried out using spectral-simulation (SS) and density-matrix (DM) methods for the 5d6s2 2D3/2−5d6s6p 4F3/20 (753.9-nm) transition that was considered by Young and Shaw [J. Opt. Soc. Am. B 12, 1398–1402 (1995)] a first-step transition in their diode-laser-initiated, resonance-ionization mass spectrometry experiments. The results from the two methods are compared with each other and with the reported experimental result. The SS result is noted to be more sensitive to the residual Doppler width but less sensitive to the laser linewidth than the DM result. It is further noted that under exact correspondence with experimental conditions, the DM result is in much better agreement with the experimental result obtained by Young and Shaw in their two-color resonant, three-photon photoionization of La by use of a narrowband, cw diode laser for the first-step excitation and a broadband, pulsed dye laser for further excitation and ionization.

Isotopic selectivity calculations for multi-step photoionization of calcium atoms using narrow-band lasers

Isotopic selectivity calculations are carried out for minor calcium isotopes against the major isotope 40Ca for the single-resonance two-step and double-resonance three-step photoionization schemes with narrow-band lasers by using spectral simulation (SS) and modified spectrum (MS) approaches. The results of these calculations are compared with the density matrix (DM) results reported in the literature. It is noted that the values of isotopic selectivity from the SS approach do not agree with those from the DM approach whereas the MS approach, considering hole burning in the Doppler-broadened atomic spectrum, predicts selectivity values which are in good agreement with the DM results. It is argued that one can adequately use the simple MS approach rather than the complex DM approach for the calculation of isotopic selectivity of multi-step photoionization with single-frequency lasers.

Trace Element Analysis using Laser Induced Breakdown Spectroscopy (LIBS) Technique

Laser‐Induced Breakdown Spectroscopy (LIBS) is well recognized as a promising tool for in situ/remote elemental analysis of environmental, archeological, clinical, and hazardous samples. With the aim of quantifying trace elements in such samples, using LIBS technique, an echelle spectrograph‐ICCD system with broad range and good resolution has been assembled. Various important parameters of this system were studied and optimized. Conditions for getting good quality LIBS spectra and signal for multielemental analysis have been achieved, and these are discussed and illustrated in this paper.

Manifestation of collective effects of laser photo-plasmas in time-of-flight mass spectrometer

The performance of Time-of-Flight Mass Spectrometer (TOF-MS) has been studied with laser produced photoions of various densities using a reflectron TOF-MS built in our laboratory. In this, the source of atoms is a resistively heated atomic beam source. As the atomic species reach the interaction region, the interaction with pulsed laser results in ions. Samarium was used as the source element to observe all its isotopes by resonant non selective excitation of one of the ground state transitions. However, as the temperature of the source is increased, the collective plasma effect of ions and electrons becomes important. As a result of this the Time-of-Flight signal (in linear mode) of Sm isotopes became poorly resolved from a well resolved condition. The number density of the ions produced in these conditions and hence the plasma parameters were calculated. The plasma parameters like Debye length (?D), the number density (ND), and frequency (fpi) confirms the collective effect. In order to avoid this undesired effect, the optimum operating condition with respect to oven temperature and laser intensity was estimated.