High-speed electronic camera reveals new ‘light-twisting’ behavior in ultra-thin material

While taking pictures with the High Speed ​​Electron Camera at the Department of Energy’s SLAC National Accelerator Laboratory, researchers discovered new behavior in an ultrathin material that offers a promising approach to manipulating light that will be useful for devices that detect, control or emit light. collectively known as optoelectronic devices, and investigating how light is polarized within a material. Optoelectronic devices are used in many technologies that touch our daily lives, including light-emitting diodes (LEDs), optical fibers, and medical imaging.

As reported in Nano LettersThe team, led by SLAC and Stanford professor Aaron Lindenberg, discovered that when oriented in a specific direction and subjected to linear terahertz radiation, an ultrathin film of tungsten ditelluride, which has desirable properties for polarizing light used in optical devices, circularly polarizes incoming light.

Terahertz radiation lies between the microwave and infrared regions of the electromagnetic spectrum and enables new ways of characterizing and controlling the properties of materials. Scientists would like to find a way to harness that light for the development of future optoelectronic devices.

Capturing the behavior of a material under terahertz light requires an advanced instrument capable of recording interactions at ultrafast speeds and SLAC’s world-leading Ultrafast Electron Diffraction (MeV-UED) instrument at the Linac Coherent Light Source (LCLS) can do that.

While MeV-UED is typically used to visualize the motion of atoms by measuring how they scatter electrons after hitting a sample with an electron beam, this new work used femtosecond electron pulses to visualize the electric and magnetic fields of incoming terahertz pulses. which caused the electrons to move back and forth. In the study, circular polarization was shown by electron images that showed a circular pattern rather than a straight line.

The ultra-thin material was only 50 nanometers thick. “That’s 1,000 to 10,000 times thinner than what we normally need to induce this kind of reaction,” Lindenberg said.

Researchers are excited about using these ultra-thin materials, known as two-dimensional (2D) materials, to make optoelectronic devices smaller and capable of more functions. They envision creating devices from layers of 2D structures, like stacking Legos, Lindenberg said. Each 2D structure will consist of a different material, precisely bonded to generate a specific type of optical response. These different structures and functionalities can be combined into compact devices that could find potential applications—for example, in medical imaging or other types of optoelectronic devices.

“This work represents another element in our toolbox for manipulating terahertz light fields, which in turn may allow new ways to control materials and devices in interesting ways,” said Lindenberg.