Laser-induced breakdown spectroscopy for remote elemental analysis of planetary surfaces.

摘要

One of the most fundamental pieces of information about any planetary body is the elemental and mineralogical composition of its surface materials. We are developing an instrument to obtain such data at ranges of up to several hundreds of meters using the technique of Laser-Induced Breakdown Spectroscopy, or LIBS. The elemental analysis is based on atomic emission spectroscopy of a laser-induced plasma or spark. A pulsed, diode-pumped ND:YAG laser of several hundred mJ optical energy is used to vaporize and electronically excite the constituent elements of a rock surface remotely located from the laser. Light emitted from the excited plasma is collected and introduced to the entrance slit of a small grating spectrometer. The spectrally dispersed spark light is detected with either a linear photo diode array or area CCD array. When the latter detector is used, the optical and spectrometer components of the LIBS instrument can also be used in a passive imaging mode to collect and integrate reflected sunlight from the same rock surface. Absorption spectral analysis of this reflected light gives mineralogical information that, when combined with the elemental analysis from the LIBS mode, provides a complete remote geochemical characterization of the rock surface. We have performed laboratory calibrations in air and in vacuum on standard rock powders to quantify the LIBS analysis. We have performed a preliminary field test using commonly available laboratory components to demonstrate remote LIBS analysis of terrestrial rock surfaces at ranges of over 25 meters. Based on these results, we believe that all major and most minor elements expected on planetary surfaces can be measured with absolute accuracy of 10--15% and much higher relative accuracy.