Terahertz researchers have developed a way to picture magnetic fields in 10-micron resolution. “It’s a world’s first,” says Dr Aurèle Adam.
Delen
Why would one want to see magnetic interaction on surfaces? Well, because almost all known interactions between electromagnetic radiation and surfaces (photons and electrons), such as take place in solar cells, cameras and displays, are merely electric phenomena. Magnetic interaction is hardly used at all. This means we could be missing out on half the fun. That’s partly because we couldn’t measure terahertz magnetic fields in enough detail to be interesting. The maximum resolution would be in the order of millimeters.
Now, that has changed. The technique that Dr Aurele Adam, from the optics group (Applied Sciences), has developed drives that resolution down by orders of magnitude to 10-20 micrometre. On top of that, he, together with his colleagues from Boston University, discovered that, locally, the magnetic field may be up to 200 times stronger than the applied field.
The (alternating) applied field consists of terahertz pulses (frequency 0,2.10^12 Hertz). Not only because this frequency range represents the group’s expertise, but also since interesting phenomena like flipping magnetic spins typically occur in the same frequency domain.
They applied the technique to a structure consisting of tiny square golden rings with 50-micron diameter, with one side cut open. These ‘resonators’ are tuned to terahertz radiation that causes an alternating current flowing through the ring, which, in turn, gives rise to a highly localised magnetic field.
The way in which the researchers have made the magnetic field visible is through the Faraday rotation: the effect is that in well-chosen materials the polarisation of incident laser light changes with the local magnetic field strength. In other words: the researchers use a laser beam to sample the local magnetic strength in minute detail.
Adam sees the resonators as a unique research tool that allows scientists to use light to switch spins, or to press magnetic properties of materials to and over their limit by the local amplification of the applied field. “It’s when you test systems to their breaking point that they may reveal their secrets.”
Aurele Adam c.s., THz near-field Faraday imaging in hybrid metamaterials, Optics Express 20, 11277-11287 (2012)
Comments are closed.