A dramatic and surprising magnetic
effect of light discovered by University of Michigan researchers
could lead to solar power without traditional semiconductor-based
Light has electric and magnetic components.
Until now, scientists thought the effects of the magnetic field were so weak that they could be ignored. What Rand and his colleagues found is that at the right intensity, when light is traveling through a material that does not conduct electricity, the light field can generate magnetic effects that are 100 million times stronger than previously expected.
Under these circumstances, the magnetic effects develop strength equivalent to a strong electric effect.
What makes this possible is a previously undetected brand of “optical rectification,” says William Fisher, a doctoral student in applied physics.
In traditional optical rectification,
light’s electric field causes a charge separation, or a pulling
apart of the positive and negative charges in a material. This sets
up a voltage, similar to that in a battery. This electric effect had
previously been detected only in crystalline materials that
possessed a certain symmetry.
The light must be shone through a material that does not conduct electricity, such as glass. And it must be focused to an intensity of 10 million watts per square centimeter.
Sunlight isn’t this intense on its own, but new materials are being sought that would work at lower intensities, Fisher said.
This new technique could make solar power cheaper, the researchers say.
They predict that with improved materials they could achieve 10 percent efficiency in converting solar power to useable energy. That’s equivalent to today’s commercial-grade solar cells.
In experiments this summer, the researchers will work on harnessing this power with laser light, and then with sunlight. The paper is titled “Optically-induced charge separation and terahertz emission in unbiased dielectrics.”
The university is pursuing patent
protection for the intellectual property.