Researchers studying rocks on Mars or suspicious white powders on the battlefield have a high-tech way to determine a sample’s chemical composition without bringing it back to the laboratory. It's known as laser-induced breakdown spectroscopy, or LIBS.
The bottom of the sea is a long way from any laboratory, so Anna Michel, a student in the MIT/WHOI Joint Program in Oceanography, would love to use LIBS on the seafloor. But Michel and other scientists in the Deep Submergence Laboratory at Woods Hole Oceanographic Institution do not have that option...at least not yet.
Invented in the 1960s, LIBS focuses high-intensity pulses of laser light on a solid, liquid, or gas until it creates plasma (the fourth state of matter) and a short-lived flash of light. Those light emissions come in different wavelengths, or “colors,” of the spectrum, depending on the elements present in the sample. A spectrometer detects the wavelengths to identify a sample’s chemical composition.
On the surface of Mars or in the deserts of Iraq, the process is relatively straightforward because rocks and dust are dry and laser light travels through air with little impediment. But at the bottom of the ocean, the intense pressure and the liquid environment suppress the plasma, producing less detectable light. The laser light and the return signal are also scattered, distorted, and diffused by seawater.
“Very few people work with LIBS in liquids,” said Michel, who has been collaborating with terrestrial LIBS expert Michael Angel of the University of South Carolina. “Even fewer people work with LIBS at high pressure, and no one has worked with it in seawater.”
A timely phone call
Alan Chave, Michel’s advisor from the WHOI Department of Applied Ocean Physics and Engineering, got a serendipitous tip on LIBS from Andrzej Miziolek, a former colleague working at the U.S. Army Research Laboratory in Aberdeen, Md. Miziolek read an article in The Baltimore Sun about ocean observing technology and called Chave to suggest that LIBS might be put to use in the sea.
The idea was to develop an instrument that could directly measure elements just as they emerge from the seafloor and spew from volcanic hydrothermal vents. For decades, ocean scientists have collected fluid samples to study underwater venting and volcanism—which build the Earth's crust, seed seawater with minerals, and fuel some of the planet’s most primeval life forms. But sampling devices on the Alvin submersible or remotely operated vehicles (ROVs) such as Jason inevitably capture excess seawater that dilutes the fluid sample's chemical composition. Other transformations also occur as samples are moved from 72 atmospheres of pressure (4,000 pounds per square inch) at the seafloor to 1 atmosphere at the water's surface.
Chave challenged Michel to adapt LIBS technology to this murky fluid environment and its crushing pressures. “With LIBS, we would be able to observe the composition of vent fluids in their natural environment, under real conditions,” Michel said.
Light in the darkness
In a black-walled, windowless room in the basement of the WHOI Deep Submergence Laboratory, Michel has been custom-designing and testing a LIBS system for the ocean floor. Alongside WHOI Assistant Scientist Sheri White (who is developing her own chemical sensors), she is brewing chemical-laden solutions to test the accuracy of her detector against what it will encounter on the seafloor. And she is learning from WHOI Senior Engineer Norman Farr, who helps her find the right lenses to focus her laser.
“Our goal is to see what elements we can detect with LIBS,” Michel said, “and then we want to build something that can be put on an underwater vehicle such as Jason.”
“Getting a light signal in liquids at high pressure is a lot harder than we thought it was going to be,” Michel said. The water (and perhaps the higher pressures, too) quench the plasma, making it harder to detect.
Michel has received a National Defense Science and Engineering Graduate fellowship to fund her graduate studies, as well as a Marine Technology Society scholarship. Last fall, her work garnered a “best student poster” prize from an Office of Naval Research-sponsored program.
Inspiring future engineers
Michel’s interest in oceanography was kindled as a teenager, when she was chosen to participate in The Jason Project, a multimedia educational program to promote interest in science and technology. She spent 10 days at sea near the Galápagos Islands, where she got a chance to help drive an ROV.
Michel is spreading that message to the next generation of female students. Along with some classmates, Michel has helped launch the MIT Women’s Initiative, a program that has received funding from MathWorks, Oracle, Raytheon, Schlumberger, and other businesses, to send female engineers to schools to talk about their careers.
“Very few women go into engineering,” she said, “because girls just don’t get the message that they should be engineers.”
Anna Michel’s research has been funded by the WHOI Ocean Ventures Fund, the WHOI Deep Ocean Exploration Institute, and the National Science Foundation.