LIBS feasibility for space missions to solar system bodies with thin and absent atmospheres

Kurzfassung

Several current and future space missions to planets, moon and asteroids in the solar system consider the landers equipped with laser-induced plasma spectroscopy (LIBS) instruments in the scientific payload. Many of the solar system bodies, which attract great interest for space research, such as planet moons and asteroids, have no or very thin atmospheres. Since instrumentation for space missions met restrictions in available mass, volume and consumed energy and since excitation and evolution of the plasma strongly depend on environmental conditions, the capability of LIBS must be studied for each individual space mission. We focus in this work on low-energy laser-induced plasma spectroscopy and demonstrate the spectroscopy capability for analysis of different geologic samples at ultra-high vacuum (below 1 mPa) and laser powers below 1 mJ. A laser developed for the ExoMars mission (Q-switched Nd:YLF, NeoLASE GmbH) operating at 1053 nm, pulse energy up to 3 mJ, has been used for plasma excitation. The investigated samples were loaded in a dedicated chamber providing atmospheric pressure down to a few nbar (hundreds of µPa) . Reduction of both pressure and a laser excitation energy results in significant decrease of the signal-to-noise ratio for most of the atomic lines (an exception are the widely broadened lines of hydrogen). However, detection of atomic emission lines of elements with relative abundances above 1E-3 (0.1 wt%), in presented samples: Al, Ca, Cr, H, K, Mg, Na, Ni, O, Si, Ti, - was possible down to a laser excitation energy of ~0.9 mJ (provided laser irradiance on a sample surface of 46 MW/mm2). 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.