LAMIS uses the energy of a high-powered laser beam to ablate a tiny spot on a sample, creating a plasma plume for spectroscopic analysis that reveals chemical elements and their isotopes.
(Image courtesy of Applied Spectra, Inc.)
At some point this year, after NASA's rover Curiosity has landed on Mars, a laser will fire a beam of infrared light at a rock or soil sample.
This will "ablate" or vaporise a microgram-sized piece of the target, generating a plume of ionised gas or plasma, which will be analysed by spectrometers to identify the target's constituent elements.
Future Mars rovers, however, will be able to do even more. Researchers with the U.S. Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), in collaboration with Applied Spectra, Inc., have developed an advanced version of this laser technology that can also analyze a target's constituent isotopes.
This expanded capability will enable future rovers for the first time to precisely date the geological age of Martian samples.
From left, Alexander Bol'shakov, Xianglei Mao and Rick Russo are part of the research team that developed LAMIS, a green chemistry laser spectroscopy technology that can be operated across vast distances. (Photo by Roy Kaltschmidt, Berkeley Lab)
Rick Russo, a scientist with Berkeley Lab's Environmental Energy Technologies Division and a pioneer in laser ablation spectroscopy, led the development of LAMIS - for Laser Ablation Molecular Isotopic Spectrometry.
As with the earlier Laser Induced Breakdown Spectroscopy (LIBS) technology being used on rover Curiosity, the basic premise is to use the energy of a high-powered laser beam focused to a tiny spot on the surface of a sample to create a plasma plume for analysis.
Each species of atoms or ions within the plasma will emit light with signature spectral emission peaks.
However, whereas LIBS only measures the optical emission spectra of atoms and ions, LAMIS measures the emission spectra of molecules and molecular ions.
This enables LAMIS to identify the specific isotopes of a chemical element within the plasma plume.
"Relative to atomic emission, molecular spectra can exhibit significantly larger isotopic shifts due to the contributions of the vibrational and rotational motion in the molecule," Russo says.
"The trick is to be patient and wait for the hot atoms and ions in the plasma to collide and merge with the ambient environment to form an oxide, or a nitride or fluoride, and then collect the molecular light emissions."
Isotopes of Strontium
Russo and his research group have been using LAMIS to study isotopes of strontium, an alkaline earth metal commonly found in geological and natural materials.
Although strontium's major isotopes are stable (strontium-90 being a notable exception), the percentage of strontium-87 will naturally increase over time as a result of the decay of radioactive rubidium.
Comparing the ratio of strontium-87 to strontium-86 is a standard tool for age dating in geochronology, oceanography and archeology. The ratio of these strontium isotopes is also used to date the origin of historic or forensic samples.
Currently, the standard means of measuring strontium isotopic ratios is by mass spectrometry technologies that involve time-consuming, labour-intensive laboratory sample dissolution work with an extensive array of instrumentation.
This sample dissolution work generates substantial chemical waste. LAMIS offers a green chemistry alternative that is faster, less expensive and can be carried out from across vast distances.
"LAMIS is not yet as sensitive or precise as mass spectrometry but unlike mass spectrometry it does not require chemical dissolution sample preparation, vacuum chambers and a laboratory infrastructure," Russo says.
"All we need is a laser beam and an optical spectrometer and we can perform real-time isotopic analyses of samples at ambient pressures and temperatures."
LAMIS represents what may be the only practical means of determining the geochronology of samples on Mars or other celestial bodies in the Solar System.
Current age estimates of such bodies suffer from uncertainties in the billions of years. That said, LAMIS also has many important applications here on Earth.
Strontium isotope ratios have been a focus in the field of medicine for both treatment and diagnostic purposes.
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