Study of sub-mJ-excited laser-induced plasma combined with Raman spectroscopy under Mars atmosphere-simulated conditions

摘要

Laser-Induced Breakdown Spectroscopy (LIBS) and Raman spectroscopy are complimentary techniques.LIBS yields elemental information while Raman spectroscopy yields molecular information about a sample,and both share similar instrumentation configurations.The combination of LIBS and Raman spectroscopy in a single instrument for planetary surface exploration has been proposed,however challenges exist for developing a combined instrument.We present LIBS and Raman spectroscopy results obtained using a diode pumped,intracavity doubled,Q-switched,Nd:YLF laser operating at 523 nm,which overcomes some of the difficulties associated with a combined instrument.LIBS spectra were obtained with 170 u J per pulse at 4 Hz repetition rate in a low pressure Mars-simulated atmosphere and Raman spectra produced with 200 mW at 100 kHz.The Nd:YLF laser is switchable between LIBS and Raman spectroscopy modes only by a change in Q-switch repetition rate.Emissions from Ca,Ca II,Fe,Fe II,Mg,Na,and O atom were identified in the mu-LIBS spectrum of oolithic hematite.Evidence was found for a change in plasma dynamics between 7 and 5 Torr that could be explained as a decrease in plasma temperature and electron density below 5 Torr.This is relevant to future Mars exploration using LIBS as the mean surface pressure on Mars varies from 3.75 to 6 Torr.LIBS plasma dynamics should be carefully evaluated at the pressures that will be encountered at the specific Mars landing site.