High-speed electron camera reveals new ‘light-bending’ behavior in ultrathin material

High-speed electron camera reveals new ‘light-bending’ behavior in ultrathin material

The snapshot taken by SLAC’s high-speed electron camera (MeV-UED), an instrument for ultrafast electron diffraction, shows evidence of circular polarization of terahertz light by an ultrathin sample of tungsten ditelluride. Source: Nano Letters (2024). DOI: 10.1021/acs.nanolett.4c00758

While taking snapshots with a high-speed electron camera at the Department of Energy’s SLAC National Accelerator Laboratory, researchers discovered a new behavior in an ultrathin material that offers a promising approach to manipulating light that would be useful for sensing, controlling or emitting light, devices that study how light is polarized in a material, collectively known as optoelectronic devices. Optoelectronic devices are used in many technologies that touch our daily lives, including light-emitting diodes (LEDs), optical fibers and medical imaging.

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

Terahertz radiation lies between the microwave and infrared regions of the electromagnetic spectrum and enables new ways to both characterize and control the properties of materials. Scientists want to find a way to use this light to develop future optoelectronic devices.

Capturing a material’s behavior under terahertz light requires an advanced device that can record interactions at ultrafast speeds, and the world-leading instrument for ultrafast electron diffraction (MeV-UED) at SLAC’s Linac Coherent Light Source (LCLS) can do exactly that.

While MeV-UED is normally used to visualize the motion of atoms by measuring how they scatter electrons after hitting a sample with an electron beam, this new study used femtosecond electron pulses to visualize the electric and magnetic fields of incoming terahertz pulses, causing the electrons to wobble back and forth. Circular polarization was demonstrated in the study, with electron images showing a circular pattern instead of a straight line

This plot shows how electrons move in a circular pattern (right) after linearly polarized terahertz radiation (left) hits thin material (center). Source: Nano Letters (2024). DOI: 10.1021/acs.nanolett.4c00758

The ultrathin material was just 50 nanometers thick. “That’s 1,000 to 10,000 times thinner than what we normally need to trigger this type of response,” Lindenberg said.

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

“This work represents a new element in our toolbox for manipulating terahertz light fields, which could enable new ways to control materials and devices in interesting ways,” Lindenberg said.

More information:
Edbert J. Sie et al., Giant Terahertz Birefringence in Ultrathin Anisotropic Semimetal, Nano Letters (2024). DOI: 10.1021/acs.nanolett.4c00758

Provided by SLAC National Accelerator Laboratory

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