Campus Physicists Find That Ground-Based Lasers Can Map Earth's Magnetic Field

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Laser Beam Technology

Courtney Moulds talks about recent findings of a new utilization of laser beam technolgy.

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A group of UC Berkeley physicists known as the Budker Group found that technology currently used in astronomy could be used to more accurately measure the Earth's magnetic field - a development that could prove useful in predicting the weather, studying geology and finding oil and minerals.

A collaboration of scientists began work on the project in 2008 after Dmitry Budker, a UC Berkeley physics professor, realized that the same sodium atoms in the atmosphere used in laser guide stars - artificial stars used as a reference point to adjust telescope optics to remove atmospheric distortion - could be employed to measure the Earth's magnetic field. Their findings were published online Monday in the scientific journal Proceedings of the National Academy of Sciences.

Princeton University physics professor William Happer first developed the idea for this technique in the early 1980s while he was working on a classified study for the Department of Defense, though the technology was not released to the public until the 1990s - after which astronomers were able to use it for adaptive optics.

However, this is the first time that scientists have thought of using the technology for the study of magnetic fields.

"I'm just very happy that finally someone is taking it seriously and going to do it," Happer said.

The new process involves emitting a strong laser beam into the mesosphere, located about 90 kilometers above the Earth's surface, where there is an abundance of sodium atoms. The laser is used to measure the rotation frequency of the sodium atoms, which are used as sensors to measure the strength of the Earth's magnetic field.

According to former UC Berkeley postdoctoral fellow James Higbie - an assistant professor of physics and astronomy at Bucknell University and a researcher in the study - "the (sodium) atoms act like a little compass needle," and in the presence of magnetic field, they spin around. Scientists can tell how fast the atoms are processing by the interaction of the atoms with the laser beam, and this speed allows them to measure the magnetic field.

The biggest advantage of this discovery, according to Higbie, is that because it is less expensive than satellites, more ground-based lasers could be implemented and used in collaboration with each other.

"The hope is that one would be able to (use this technology) with many of these things in parallel," Higbie said. This would allow for "greater coverage and more ability to monitor the field."

Furthermore, satellites that are currently used for this purpose are sent into space to avoid magnetization on Earth, but certain metals within the satellites themselves can affect accuracy, as can the fact that the satellites are constantly moving. The ground-based laser technology could avoid both of these problems.

Creating maps of the Earth's magnetic field is important for several reasons, including geology, studies of ocean currents, climatology and oil and mineral exploration.

"Large-scale measurements of the earth's magnetic field are one of the only means of gaining direct information about what is happening below the earth's surface," said UC Berkeley alumnus Dr. Simon Rochester, a co-author of the study, in an e-mail. "These measurements can also be used to study phenomena occurring outside the earth's atmosphere."

Team member and UC Berkeley postdoctoral fellow Brian Patton said that if they "were able to come up with more sensitive magnetic detectors," magnetic resonance imaging could be conducted outside of a strong magnet.

He added that it would be interesting to study the magnetic field near earthquake fault lines to see if magnetic fields indicate active faults.


Contact Courtney Moulds at [email protected]

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