Leon J. Radziemski

Time-Resolved Laser-Induced Breakdown Spectrometry for the Rapid Determination of Beryllium in Beryllium-Copper Alloys

Time-resolved laser-induced breakdown spectrometry has been combined with the long spark technique and applied to the rapid determination of beryllium in beryllium-copper alloys. A calibration curve was developed which related the beryllium concentration in a solid copper matrix to the Be(I) 234.9-nm to Cu(II) 235.7-nm intensity ratio. The beryllium concentrations ranged from 0.001 to 0.22%. For the lowest concentration the relative standard deviation of replicate samples was 7%, implying a detection limit of 0.0002% (2 ppm) at a signal-to-noise ratio of 3. The excitation temperature was determined from Boltzmann plots on Cu(I) and Cu(II), assuming local thermodynamic equilibrium. The values from the two spectra agreed well, and averaged to 13,850 K at 1 μS into the plasma lifetime.

Measurement of the properties of a CO2 laser induced air-plasma by double floating probe and spectroscopic techniques

Abstract The laser-induced breakdown spark has recently been advanced as a method for real-time, in-situ spectrochemical analysis of gases. Many of these analyses take place in ambient air. To better characterize this source, we have measured the temporal variation of temperature and electron density in an air plasma induced by a CO 2 laser operating at 0.5 and 0.8 J/pulse. The electron temperature was measured by the double floating-probe technique (DFP). An excitation temperature for oxygen atoms was determined spectroscopically by Boltzmann plots. Electron density in the plasma was measured from the Stark broadening of the 715.6-nm line of 01. At 0.5 J/pulse, the DFP temperature ranged from 175000 K at 5 μs to less than 10000 K at 25 μs, while the 01 excitation temperature ranged from 19000 K at 1 μs to above 11 000 K at 25 μs. The excitation temperature and electron density agree with values calculated by others from local thermodynamic equilibrium models of an air plasma. While the electron temperature from the DFP method is much higher than the excitation temperature at 5 μs, at times greater than 25 μs the two have converged, implying thermodynamic equilibration between the species.

Direct determination of copper in solids and ores by laser ablation-direct current argon plasma emission spectrometry

The use of a laser ablation-direct current argon plasma emissions spectrometric system for the direct determination of metals in solids is described. Sample preparation of solid steel samples involves machining to fit the geometry of the ablation chamber. A cellulose binder and copper ore are mixed thoroughly in a ball mill to ensure homogeneity and pelletized in a press at 20,000 psi to fit the geometry of the ablation chamber. Copper, manganese, and nickel are determined using the system on standard steel samples, and copper is determined in pelletized copper ore with good agreement obtained with certified values. Precisions are typically in the 3 - 10% range with a detectable limit of 100 g g of copper. 6 references, 4 figures, 2 tables.

Resonance-enhanced multiphoton ionization of N2 at 193 and 248 nm detected by N2+ fluorescence

Abstract Using a broad band excimer laser operating at 193 and 248 nm multiphoton ionization of N 2 at high pressures in air and pure nitrogen has been detected by fluorescence from N 2 + in the B-X first negative system. Measurements of the fluorescence intensity as a function of beam irradiance indicate resonances in N 2 at the energy of two 193 nm photons (2 + 1 REMPI) and three 248 nm photons (3 + 1 REMPI). Possible resonant intermediate states are discussed.

LASER-INDUCED BREAKDOWN SPECTROSCOPY: PRINCIPLES, APPLICATIONS, AND INSTRUMENTS

Laser-induced breakdown spectroscopy (LIBS) has been used for a variety of applications, usually those requiring remote or in situ spectrochemical analysis. Several beryllium monitoring instruments based on LIBS have been built. The progress and implementation of this technique will be reviewed.

On the coupling of blast wave theory with atomic excitation in low-energy laser-induced plasmas formed in gases

Time‐dependent intensities of the spectral lines emitted by laser‐induced plasmas generated in several gases are presented. The time‐resolved and spatially varying intensities of two once‐ionized nitrogen lines were used to calculate radial temperature distribution of temperature within the plasma. A modified blast wave theory, in which ionization was included through the Saha equation and the equation of conservation of charge, was used to calculate time‐dependent intensities of several spectral lines of C, N, He, and Ar. The temporal profiles of the spectral lines appear to be dependent on the ionization potentials of the species in the plasma.

Modeling of time-dependent laser-induced plasma spectra formed on a carbon surface

The blast wave theory coupled with ionization described by the Saha equations and the charge conservation equation, are used to calculate the time‐dependent, spatial distribution of the number densities of the different species of a plasma formed on a carbon surface. The temporal behavior of the normalized intensity profiles of the C i (247.8 nm) and C ii (251.1 nm) lines and the Stark shifts of the C i (247.8 nm) line from 0.1 to 0.4 μs are obtained. Good agreement is found between theoretical and experimental time‐dependent, normalized, line intensity profiles and Stark shift profiles.

Absolute excited state and ion densities from two- and three-photon processes in some 6p levels of atomic krypton

Neutral krypton atoms are excited from the ground state to the 4p56p[3/2]2 state by two‐photon absorption from an ArF excimer laser operating at 193.41 nm. The third photon ionizes the krypton atoms. Excitation and ionization yields are theoretically computed employing the standard laser rate‐equations analysis. Measurements are made on both the excitation and ionization yields. The experimental results are in good agreement with the theoretical predictions of our formulations, as well as with those of other authors.

Time Resolved Laser-Induced Breakdown Spectrometry For Rapid Alloy Analysis

Time-resolved laser-induced breakdown spectrometry has been combined with the long spark technique and applied to the rapid determination of beryllium in beryllium-copper alloys. Excitation temperatures within the spark were determined from Boltzmann plots on Cu and Cu lines. The method can be extended to other elements in other matrices, even non-conductors.

On The Use Of Multiple Photon Processes In Krypton For Laser Guiding Of Electron Beams

Neutral krypton atoms were excited from the ground state 4p6 1S0 to the 4p5 6p[3/2]2 state by a resonant two-photon absorption from a line- narrowed ArF excimer laser operating at 193.41 nm. A third photon, absorbed while the atom is in the excited state, ionizes it. Excited state and ion densities were theoretically computed using a stvdard,rate-equation analysis. The irradiance levels used (1-5x10 8 W/cm2) were too low for significant ground and excited state ac Stark and Rabi effects. The photon detection system was calibrated with a standard tungsten lamp. Ion signals wel3 measured with known electrical components. The resonance results were compared with predictions of non-resonant ionization based on a standard formulation. The ion and excited state densities have been used with a modified electron beam propagation code (IPROP) to model such propagation in a low pressure laser-excited krypton channel. The modifications included the effects to field ionization of the excited krypton atoms. Implications for guiding of e-beams using ArF excited krypton are discussed.