A team of scientists and engineers from the University of Wisconsin-Madison, the University of Southern California, and Washington University in St. Louis has developed a groundbreaking material capable of splitting an infrared light beam into two separate directions. This crystal exhibits the highest degree of “double refraction” ever recorded on Earth, surpassing the team’s previous achievement. The material, called strontium titanium sulfide (STS), has the potential to revolutionize various applications such as night vision, lidar, chemical detection, and microscopy.

Refraction occurs when light travels from one substance to another, causing a change in its direction. Double refraction occurs when light enters an anisotropic material with varying properties in different directions, splitting into two rays that travel in separate directions. The difference in the refractive indices in these two directions is known as birefringence. The team was surprised to discover that the birefringence of STS was three times higher than that of its predecessor, barium titanium sulfide (BTS), despite having a similar structure.

Upon closer examination, it was found that STS had a larger repeating structure due to the presence of some additional strontium atoms. This unexpected atomic-level change resulted in an improved refractive index along one direction of the material. Researchers believe that this observation opens possibilities to find similar materials in which small external stimuli, such as bending or heating, can dynamically alter the material’s optical response. This discovery could lead to new classes of adjustable optical applications.

Although the current synthesis method only produces small flakes of STS, efforts are underway to refine the process and create larger single-crystal versions of the material. This breakthrough in achieving unprecedented double refraction highlights the potential for future advancements in the field of optics.

– Advanced Materials (2023). DOI: 10.1002/adma.202303588