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a b s t r a c tWe report on efforts to perform theoretical modeling of the emission spectrum measured from a basalt sample. We compare our calculations with measurements that were made to provide standards for the ChemCam instrument on the Mars Science Laboratory. We find that to obtain good agreement between modeling and the measurement, it is necessary to determine atomic and ionic level populations via a multi-element approach in which the free electron density that is created influences all the species within the plasma. Calculations that consider each element separately are found to be in poorer agreement with the measured spectrum, indicating that the 'matrix effect' term often used to describe the influence of other species on the emission spectrum from a given element is due to the influence of the global electron density of the plasma. We explore the emission features in both the visible and near-infrared wavelength ranges, and also examine radiation transport effects for some of the most intense features found in the basalt spectrum. Finally, we also provide comparisons of the ChemCam measurement with new high-resolution spectral measurements.

Laser induced breakdown spectroscopy (LIBS) is a rapid atomic emission spectroscopy technique that can be configured for a variety of applications including space, forensics, and industry. LIBS can also be configured for stand-off distances or in-situ, under vacuum, high pressure, atmospheric or different gas environments, and with different resolving-power spectrometers. The detection of uranium in a complex geological matrix under different measurement schemes is explored in this paper. Although many investigations have been completed in an attempt to detect and quantify uranium in different matrices at in-situ and standoff distances, this work detects and quantifies uranium in a complex matrix under Martian and ambient air conditions. Investigation of uranium detection using a low resolving-power LIBS system at stand-off distances (1.6m) is also reported. The results are compared to an in-situ LIBS system with medium resolving power and under ambient air conditions. Uranium has many thousands of emission lines in the 200-800nm spectral region. In the presence of other matrix elements and at lower concentrations, the limit of detection of uranium is significantly reduced. The two measurement methods (low and high resolving-power spectrometers) are compared for limit of detection (LOD). Of the twentyone potential diagnostic uranium emission lines, seven (409, 424, 434, 435, 436, 591, and 682 nm) have been used to determine the LOD for pitchblende in a dunite matrix using the ChemCam test bed LIBS system. The LOD values determined for uranium transitions in air are 409.013 nm (24700 ppm), 424.167 nm (23780 ppm), 434.169 nm (24390 ppm), 435.574 nm (35880 ppm), 436.205 nm (19340 ppm), 591.539 nm (47310 ppm), and 682.692 nm (18580 ppm). The corresponding LOD values determined for uranium transitions in 7 torr CO 2 are 424.167 nm (25760 ppm), 434.169 nm (40800 ppm), 436.205 nm (32050 ppm), 591.539 nm (15,340 ppm), and 682.692 nm (29080 ppm). The LOD values determine for uranium emission lines using the medium resolving power (10000 λ/ λ) LIBS system for the dunite matrix in air are 409.013 nm (6120 ppm), 424.167 nm (5356 ppm), 434.169 nm (5693 ppm), 435.574 nm (6329 ppm), 436.205 nm (2142 ppm), and 682.692 nm (10741 ppm). The corresponding LOD values determined for uranium transitions in a SiO 2 matrix are 409.013 nm (272 ppm), 424.167 nm (268 ppm), 434.169 nm (402 ppm), 435.574 nm (1067 ppm), 436.205 nm (482 ppm), and 682.692 nm (720 ppm).The impact of spectral resolution, atmospheric conditions, matrix elements, and measurement distances on LOD are discussed. The measurements will assist one in selecting the proper system components based upon the application and the required analytical performance.

The goal of this work was to investigate the matrix effect of copper in the presence of sodium or magnesium in a laser-induced plasma. Varying amounts of copper were mixed and pressed with a constant amount of sodium or magnesium and a stearic acid binder. Experimental parameters such as delay time and laser pulse energy were varied to observe trends in the emission intensity of the Na I 588.99 nm, Na I 589.59 nm, Mg I 277.98 nm, and Mg II 279.08 nm lines. Experimental observations are supported by theoretical calculations and modeling that show the Na I and Mg I emission intensities increase in the presence of copper while the Mg II line intensity decreases due to the increase in electron density (Ne) of the plasma when copper is added. The increase in electron density changes the population of the atomic species within the plasma through an increase in recombination of ions with electrons, shifting the populations toward more neutral states, providing an explanation for the observed matrix effects found in these, and many previous, studies.

This Letter presents a novel approach to study electron transport in warm dense matter. It also includes the first x-ray Thomson scattering (XRTS) measurement from low-density CH foams compressed by a strong laser-driven shock at the OMEGA laser facility. The XRTS measurement is combined with velocity interferometry (VISAR) and optical pyrometry (SOP) providing a robust measurement of thermodynamic conditions in the shock. Evidence of significant preheat contributing to elevated temperatures reaching 17.5-35 eV in shocked CH foam is measured by XRTS. These measurements are complemented by abnormally high shock velocities observed by VISAR and early emission seen by SOP. These results are compared to radiation hydrodynamics simulations that include first-principles treatment of nonlocal electron transport in warm dense matter with excellent agreement. Additional simulations confirm that the x-ray contribution to this preheat is negligible.