Characterization of Laser-Induced Breakdown Spectroscopy (LIBS) for Application to Space Exploration

Abstract

Early in the next century, several space missions are planned with the goal of landing craft on asteroids, comets, the Moon, and Mars. To increase the scientific return of these missions, new methods are needed to provide (1) significantly more analyses per mission lifetime, and (2) expanded analytical capabilities. One method that has the potential to meet both of these needs for the elemental analysis of geological samples is laser-induced breakdown spectroscopy (LIBS). These capabilities are possible because the laser plasma provides rapid analysis and the laser pulse can be focused on a remotely located sample to perform a stand-off measurement. Stand-off is defined as a distance up to 20 m between the target and laser. Here we present the results of a characterization of LIBS for the stand-off analysis of soils at reduced air pressures and in a simulated Martian atmosphere (5–7 torr pressure of CO2) showing the feasibility of LIBS for space exploration. For example, it is demonstrated that an analytically useful laser plasma can be generated at distances up to 19 m by using only 35 mJ/pulse from a compact laser. Some characteristics of the laser plasma at reduced pressure were also investigated. Temporally and spectrally resolved imaging showed significant changes in the plasma as the pressure was reduced and also showed that the analyte signals and mass ablated from a target were strongly dependent on pressure. As the pressure decreased from 590 torr to the 40–100 torr range, the signals increased by a factor of about 3–4, and as the pressure was further reduced the signals decreased. This behavior can be explained by pressure-dependent changes in the mass of material vaporized and the frequency of collisions between species in the plasma. Changes in the temperature and the electron density of the plasmas with pressure were also examined and detection limits for selected elements were determined.

Laser Induced Breakdown Spectroscopy

“…However, due to the higher throughput of optical filters (there is no slit) in relation to dispersive spectrographs, modern tunable filters, such as acousto-optical tunable filters (AOTF), have been used in LIBS for plasma imaging, at a particular line emission, using bi-dimensional detecting systems. 45,[148][149][150] An AOTF is an optical band pass filter based on a diffraction of the radiation by an acoustic wave, whose frequency determines the selected wavelength, propagating through an isotropic or anisotropic crystal medium (depending on the wavelength range of the AOTF). 151 Plasma imaging using AOTF has been used for investigating the spatial and temporal distribution of atomic and ionic lines, 45 the effect of the focusing lens, the lens to sample distance, the angle of incidence of the laser pulse onto the sample, 45,148 and the effect of Figure 7.…”

“…3, 2007 atmospheric pressure on the size and shape of the resulting plasma. 149 Another type of tunable filter, called liquid crystal tunable filter (LCTF), has also been employed for plasma imaging. 150 The LCTF is a birefringent filter based on the constructive interference of theoretically just one wavelength, which is transmitted through the device, and destructive interferences of all others by different phase retardation between the ordinary and the extraordinary radiation rays passing through a liquid crystal.…”

“…Knight et al 149 presented the results of the characterization of LIBS for the stand-off analysis of soils at reduced air pressures and in a simulated Martian atmosphere (6.58×10 -3 -9.21×10 -3 atm pressure of CO 2 ). In this work, under Martian conditions, the analyte signals appear to be somewhat enhanced over those recorded at atmospheric pressure due to increased ablation.…”

Spectroscopic characterization of laser-induced tin plasma

“…Laser-induced plasma ͑LIP͒ techniques are also used in space applications such as in chemical sensors for the exploration of Mars and micropropulsion for satellite positioning, as well as in the detection of biological molecules. 3,4 Other important applications of LIP include pulsed laser deposition, 5 nanoparticle and cluster production, 6,7 and laser-induced breakdown spectroscopy ͑LIBS͒. 8 Laser-created plasma characteristics are strongly dependent upon several key parameters, including laser intensity, pulse duration and wavelength, target material and geometry, and the nature and pressure of any ambient gas.…”

Improved Analytical Characterization of Solid Waste-Forms by Fundamental Development of Laser Ablation Technology

“…Personnel exposure to hazardous materials will be minimized. Laboratory is investigating direct soil, waste-form, and plutonium characterization using laser ablation plasma emission (LIBS) and ICP-MS (19)(20)(21). Savannah River also has investigated laser-ablation ICP-MS for the characterization of vitrified waste glass (22,23).…”