James E. Barefield

Remote Elemental Analysis by Laser-Induced Breakdown Spectroscopy Using a Fiber-Optic Cable

The elemental composition of solids can be determined rapidly and simply with the use of laser-induced breakdown spectroscopy (LIBS). This method, described in detail elsewhere, uses powerful laser pulses to form a microplasma or spark on a sample. A small amount of material is vaporized, and emitting species in the plasma are identified by spectrally and temporally resolving the spark light. Although LIBS measurements can be performed remotely on solids at distances up to 24 m from the laser and detection system with a long-focal-length lens, this method has some disadvantages including safety (the possibility of ocular damage by the high-energy laser pulses), need for a clear line of sight to the analysis area, scattering of incident pulse energy by dusts or fogs, and problems associated with precise focusing of laser beams at long distances. In particular, the plasma will preferentially form on dust particles in front of the sample because of the long Rayleigh length of the focused beam.

Calibrating the ChemCam laser-induced breakdown spectroscopy instrument for carbonate minerals on Mars

The ChemCam instrument suite onboard the NASA Mars Science Laboratory rover includes the first laser-induced breakdown spectroscopy (LIBS) instrument for extraterrestrial applications. Here we examine carbonate minerals in a simulated martian environment to better understand the LIBS signature of these materials on Mars. Both chemical composition and rock type are determined using multivariate analysis techniques. Composition is confirmed using scanning electron microscopy. Our results show that ChemCam can recognize and differentiate between different types of carbonate materials on Mars.

Time-resolved remote Raman study of minerals under supercritical CO2 and high temperatures relevant to Venus exploration

We report time-resolved (TR) remote Raman spectra of minerals under supercritical CO2 (approx. 95 atm pressure and 423 K) and under atmospheric pressure and high temperature up to 1003 K at distances of 1.5 and 9 m, respectively. The TR Raman spectra of hydrous and anhydrous sulphates, carbonate and silicate minerals (e.g. talc, olivine, pyroxenes and feldspars) under supercritical CO2 (approx. 95 atm pressure and 423 K) clearly show the well-defined Raman fingerprints of each mineral along with the Fermi resonance doublet of CO2. Besides the CO2 doublet and the effect of the viewing window, the main differences in the Raman spectra under Venus conditions are the phase transitions, the dehydration and decarbonation of various minerals, along with a slight shift in the peak positions and an increase in line-widths. The dehydration of melanterite (FeSO4 · 7H2O) at 423 K under approximately 95 atm CO2 is detected by the presence of the Raman fingerprints of rozenite (FeSO4 · 4H2O) in the spectrum. Similarly, the high-temperature Raman spectra under ambient pressure of gypsum (CaSO4 · 2H2O) and talc (Mg3Si4O10(OH)2) indicate that gypsum dehydrates at 518 K, but talc remains stable up to 1003 K. Partial dissociation of dolomite (CaMg(CO3)2) is observed at 973 K. The TR remote Raman spectra of olivine, α-spodumene (LiAlSi2O6) and clino-enstatite (MgSiO3) pyroxenes and of albite (NaAlSi3O8) and microcline (KAlSi3O8) feldspars at high temperatures also show that the Raman lines remain sharp and well defined in the high-temperature spectra. The results of this study show that TR remote Raman spectroscopy could be a potential tool for exploring the surface mineralogy of Venus during both daytime and nighttime at short and long distances.

Analysis and spectral assignments of mixed actinide oxide samples using laser-induced breakdown spectroscopy (LIBS).

In this paper, we report for the first time the identification and assignments of complex atomic emission spectra of mixed actinide oxides using laser-induced plasma spectroscopy or laser-induced breakdown spectroscopy (LIBS). Preliminary results of LIBS measurements on samples of uranium dioxide (UO2)/plutonium dioxide (PuO2) and UO2/PuO2/americium dioxide (AmO2)/neptunium dioxide (NpO2) simulated fuel pellets (or mixed actinide oxide samples) are reported and discussed. We have identified and assigned >800 atomic emission lines for a UO2/PuO2/AmO2/NpO2 fuel pellet thus far. The identification and assignments of spectral emission lines for U, Pu, and Am are consistent with wavelength data from the literature. However, only a few emission lines have been assigned with a high degree of confidence for Np compared with atomic emission data from the literature. We also indicate where atomic emission lines for Cm would most likely appear in the spectral regions shown. Finally, we demonstrate that a LIBS system with a resolving power of approximately 20 000 is adequate for analyzing complex mixtures of actinide elements within the same sample.

Remote-Raman spectroscopic study of minerals under supercritical CO2 relevant to Venus exploration.

The authors have utilized a recently developed compact Raman spectrometer equipped with an 85 mm focal length (f/1.8) Nikon camera lens and a custom mini-ICCD detector at the University of Hawaii for measuring remote Raman spectra of minerals under supercritical CO(2) (Venus chamber, ∼102 atm pressure and 423 K) excited with a pulsed 532 nm laser beam of 6 mJ/pulse and 10 Hz. These experiments demonstrate that by focusing a frequency-doubled 532 nm Nd:YAG pulsed laser beam with a 10× beam expander to a 1mm spot on minerals located at 2m inside a Venus chamber, it is possible to measure the remote Raman spectra of anhydrous sulfates, carbonates, and silicate minerals relevant to Venus exploration during daytime or nighttime with 10s integration time. The remote Raman spectra of gypsum, anhydrite, barite, dolomite and siderite contain fingerprint Raman lines along with the Fermi resonance doublet of CO(2). Raman spectra of gypsum revealed dehydration of the mineral with time under supercritical CO(2) at 423 K. Fingerprint Raman lines of olivine, diopside, wollastonite and α-quartz can easily be identified in the spectra of these respective minerals under supercritical CO(2). The results of the present study show that time-resolved remote Raman spectroscopy with a compact Raman spectrometer of moderate resolution equipped with a gated intensified CCD detector and low power laser source could be a potential tool for exploring Venus surface mineralogy both during daytime and nighttime from a lander.

Observation and analysis of fundamental bending mode of T2O

Abstract The absorption spectrum of the ν 2 band of T 2 O vapor has been observed at 0.04 cm −1 resolution. A total of 549 transitions has been assigned; 474 of these have been used to evaluate the rotational constants A , B , and C as well as the fourth-order and sixth-order distortion constants and one eighth-order constant for the upper vibrational state.

Analysis of the fundamental asymmetric stretching mode of T2O

Abstract The ν 3 mode of T 2 O, observed at 0.04 cm −1 , has been analyzed. By an iterative process of fitting and assignment 210 lines were assigned; 167 of these were used in the final fitting. The standard deviation of the fit is 0.023 cm −1 . The rotational constants, A , B , and C , as well as the quartic distortion constants, have been evaluated for the excited state.

Analysis of the ν1 fundamental mode of HTO

Abstract The ν1 mode of HTO, observed at 0.04 cm−1 resolution, has been analyzed. By an iterative process of fitting and assignment 244 lines were assigned and used in a final fitting, together with 48 previously observed pure rotational transitions. The standard deviation of the combined fit was 0.0017 cm−1. The rotational constants, quartic centrifugal distortion constants, and four sextic centrifugal distortion constants were determined for the excited state.

A Spectroscopic Investigation of the Electronic Structure of Neptunyl Ions

Emission spectra of NpO2Cl42− doped in a Cs2ZrCl6 matrix have been measured between 6000 and 7200 cm-1. An f-f transition has been assigned, and vibronic structure on this origin is reported. These electronic and vibrational energies are compared with previous studies including the theoretical work of Pitzer and co-workers, and the spectroscopic work of Denning and co-workers.

Laser-induced breakdown spectroscopy using mid-infrared femtosecond pulses

We report on a laser-induced breakdown spectroscopy (LIBS) experiment driven by mid-infrared (2.05-μm) fs pulses, in which time-resolved emission spectra of copper were studied. Ab-initio modeling is consistent with the results of new fs measurements at 2.05 μm and traditional 800-nm fs-LIBS. Ablation by mid-infrared fs pulses results in a plasma with a lower plasma density and temperature compared to fs-LIBS performed at shorter laser wavelength. LIBS driven by mid-infrared fs pulses results in a signal-to-background ratio ∼50% greater and a signal-to-noise ratio ∼40% lower than fs-LIBS at near-infrared laser wavelength.