Mathematics – Logic
Scientific paper
Dec 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011agufm.p33a1757p&link_type=abstract
American Geophysical Union, Fall Meeting 2011, abstract #P33A-1757
Mathematics
Logic
[1060] Geochemistry / Planetary Geochemistry, [5410] Planetary Sciences: Solid Surface Planets / Composition, [5494] Planetary Sciences: Solid Surface Planets / Instruments And Techniques
Scientific paper
Elemental analysis of geologic samples based on atomic emission spectroscopy is currently considered for several future space lander missions to planets, moons and asteroids in solar system. The spectroscopic techniques, called laser-induced plasma (breakdown) spectroscopy (LIBS), provides quantitatively the microscopic in-situ abundances of all major and many trace elements of surfaces of solar system bodies. Excitation and evolution of the plasmas induced by lasers depend on the properties of the investigated material and on environmental conditions. This study focuses on the feasibility of spectroscopy of plasmas induced by low-energy laser (below 1 mJ per pulse) for the exploration of solar system bodies with thin atmospheres (pressures below 1 mPa). At such low pressures the excited plasmas have small plumes and expand very rapidly, which limits both the LIBS signal intensity and the available acquisition time. This, in turn, requires usually relatively powerful laser sources to create a detectable LIBS plasma. The low pressure conditions are simulated in a dedicated chamber at the DLR-Berlin Institute of Planetary Research, that can hold the Martian-like atmosphere or high vacuum conditions. Two infrared Q-switched lasers are used for comparative investigation of atomic emission spectra: Firstly, a Nd:YAG laser (Inlite, Continuum) operating at 1064 nm and at 10 Hz, pulse energy up to 230 mJ at 8-10 ns pulse duration and, secondly, developed for future planetary missions Nd:YLF laser (NeoLASE) operating at 1053 nm and at 10-50 Hz, pulse energy up to 3 mJ at 3-5 ns pulse duration. The emitted light of the laser-induced plasma is analysed by an echelle spectrometer (LTB Aryelle Butterfly) covering the wavelength range of 280-900 nm with a spectral resolution of around 104. Identification of atomic transitions is performed using the LTB built-in spectrometer software by comparison with the NIST spectral database. Several basaltic rock and sediment standards were crushed to powder and pressed into pellets. Reduction of both pressure and laser excitation energy results in a significant decrease of the signal-to-noise ratio for most atomic lines (an exception are the widely broadened lines of H). However, the detection of atomic emission lines of elements with relative abundances above 10-3 (0.1 wt%) - Al, Ca, Cr, H, K, Mg, Mn, Na, Ni, O, Si, Ti, - is possible down to a laser excitation energy of 0.9 mJ (laser irradiance on the sample surface 46 MW/mm2). Additionally, the detection of carbon and sulphur, having strong atomic transitions in ultraviolet range, can be expected by extension of the spectral range of the LIBS spectrometer to 190 nm. Atomic doublet and triplet transitions, broadened by atomic collisions at ambient pressures (100 kPa), become spectrally resolved and are identified below 1 mPa. This demonstrates the feasibility of miniaturized laser-induced breakdown spectrometry for space missions to solar bodies with absent or thin atmospheres.
Hubers H.
Jessberger Elmar
Pavlov Sergey
Schrã¶der S.
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