Ground-based lasers vie with satellites to map Earth's magnetic field

Ground-based lasers vie with satellites to map Earth's magnetic field: It is well known that these sodium atoms are affected by the Earth's magnetic field. Budker, who specializes in extremely precise magnetic-field measurements, realized that you could easily determine the local magnetic field by exciting the atoms with a pulsed or modulated laser of the type used in guide stars. The method is based on the fact that the electron spin of each sodium atom precesses like a top in the presence of a magnetic field. Hitting the atom with light pulses at just the right frequency will cause the electrons to flip, affecting the way the atoms interact with light.
"It suddenly struck me that what we do in my lab with atomic magnetometers we can do with atoms freely floating in the sky," he said.