The clear mineral Iceland spar can make you see double if you place the mineral on top of an image due to an occurrence of double refraction. This double refraction is a result of a crystal material quality known as optical anisotropy (meaning directional dependence).
Light slows down, and the beams bend predictably by different amounts when it passes through various materials depending on the materials optical anisotropy. Materials with optical anisotropy are crucial for a variety of devices including microscopes, lasers, lens filters, and liquid-crystal displays. Usually, devices that alter light polarization employ materials with optical anisotropy.
A group of scientists and engineers led by the University of Wisconsin–Madison, and University of Southern California have made a crystal of a compound combining barium, titanium and sulfur (BaTiS3), that has a higher degree of optical anisotropy than all other solid materials on earth. This optical anisotropy was found to be extraordinarily high for infrared light. The team described the new material in a paper published in the journal Nature Photonics.
Imaging and other types of remote sensing employing a mid-infrared transparency window are potential applications for the new material. The researchers speculate that the new material might also be useful in energy-harvesting photovoltaic cells or LEDs. According to the researchers, the new crystal boasts roughly 50 to 100 times greater optical birefringence (a metric of anisotropy) for mid-infrared light than has been measured before.
Unique Molecular Structure Enables Material to Split Light
A unique molecular structure made of long chains of atoms arranged in parallel rows gives the material that light-splitting capability. Employing advanced computational methods, the researchers meticulously selected rows of atoms, precisely grew them in the lab, and carefully studied them.
In the future, the team plans to investigate other properties of the new material as they also attempt to develop processes to synthesize it in large quantities.
The project was a group effort involving researchers at multiple institutions with varied expertise. The scientists are filing a patent on the material through USC and the Wisconsin Alumni Research Foundation at UW–Madison. Other contributors included scientists at the Air Force Research Laboratory at Wright-Patterson Air Force Base and the University of Missouri.
This research was supported by grants from the Link Foundation Energy Fellowship, the U.S. Air Force Office of Scientific Research (FA9550-16-1-0335 AND FA9550-15RXCOR198), the Army Research Office (W911NF-16-1-0435), the Office of Naval Research (N00014-16-1-2556), the National Science Foundation (ECCS- 1653870), and the Department of Energy (DE-SC0001299, DE-FG02-09ER46577 AND DE-FG02–07ER46376).
S., Niu, G. Joe, Zhao, H., Zhou, Y., et al. Giant optical anisotropy in a quasi-one-dimensional crystal, Nature Photonics, 18, June 2018. https://doi.org/10.1038/s41566-018-0189-1