Scientists have created a new magnetic field detector that is highly sensitive and 1,000 times more energy efficient than those available today.
The innovation could lead to tiny battery-powered devices that could be used in medical imaging, contraband detection, and could even have applications in geological exploration, Massachusetts Institute of Technology (MIT) reported.
Current devices that are used in these fields rely on gas-filled chambers or can only operate in narrow frequency bands, these new detectors employ synthetic diamonds with nitrogen vacancies (NVs), which are extremely sensitive to magnetic fields. A diamond chip about the size of a thumbnail could hold trillions of nitrogen vacancies, each of which can perform its own measurement of a magnetic field. In the past it has been difficult for scientists to aggregate such a high number of measurements. To determine these measurements researchers must zap the nitrogen vacancies with a laser light, the intensity of which reveals the magnetic state.
"In the past, only a small fraction of the pump light was used to excite a small fraction of the NVs," said Dirk Englund, the Jamieson Career Development Assistant Professor in Electrical Engineering and Computer Science and one of the designers of the new device. "We make use of almost all the pump light to measure almost all of the NVs."
A nitrogen vacancy is a missing atom in the lattice of a crystal; electrons in this vacancy have the ability to interact with magnetic fields, making them ideal for sensing. When a photon strikes an electron in this nitrogen vacancy, it is boosted into a higher energy state, and could release its excess energy as a photon. Magnetic fields can flip the electron's magnetic orientation, which widens the difference between the two energy states. Making accurate measurements with this type of device requires the scientists to collect a high number of photons.
"Only a small fraction of the light is absorbed," said Hannah Clevenson, a graduate student in electrical engineering. "Most of it just goes straight through the diamond. We gain an enormous advantage by adding this prism facet to the corner of the diamond and coupling the laser into the side. All of the light that we put into the diamond can be absorbed and is useful."
The team calculated the angle at which a laser should enter a crystal so that it will stay confined, but bounce around like a "cue ball" before its energy is completely absorbed. The geometry of the nitrogen vacancies allows the photons to emerge at four different angles, to be collected by a lens at the end of the crystal. This technique allows 20 percent of the photons to be focused onto a light detector, facilitating a reliable measurement.
The findings were published in a recent edition of the journal Nature Physics.
