The researchers used a stack of rotating metasurface devices to capture the spectral and polarization details of thermal radiation as well as intensity information acquired with traditional thermal imaging. Credit: Xueji Wang, Purdue University
Researchers have developed a new technology that uses meta-optical devices to perform thermal imaging. This approach provides richer information about imaged objects, which could expand the use of thermal imaging in areas such as autonomous navigation, security, thermography, medical imaging and remote sensing.
“Our method overcomes the challenges of traditional spectral thermal imagers, which are often large and delicate due to their reliance on large filter wheels or interferometers,” said Zubin Jacob, research team leader of the Purdue University. “We have combined meta-optical devices and cutting-edge computer imaging algorithms to create a system that is both compact and robust while having a wide field of view.”
In Optical, the authors describe their novel spectro-polarimetric decomposition system, which uses a stack of rotating metasurfaces to decompose thermal light into its spectral and polarimetric components. This allows the imaging system to capture the spectral and polarization details of thermal radiation in addition to the intensity information acquired with traditional thermal imaging.
The researchers showed that the new system can be used with a commercial thermal camera to successfully classify various materials, a task typically difficult for conventional thermal cameras. The method’s ability to distinguish temperature variations and identify materials based on spectro-polarimetric signatures could help enhance safety and efficiency for various applications, including autonomous navigation.
“Traditional autonomous navigation approaches rely heavily on RGB cameras, which struggle in difficult conditions like low light or bad weather,” said the paper’s first author, Xueji Wang, a postdoctoral researcher at the Purdue University.
“When integrated with heat-assisted detection and ranging technology, our spectro-polarimetric thermal camera can provide vital information in these challenging scenarios, delivering clearer images than conventional RGB or thermal cameras. Once we achieve real-time video capture, the technology could significantly improve scene awareness and overall safety.
Do more with a smaller imager
Long-wave infrared spectro-polarimetric imaging is crucial for applications such as night vision, machine vision, trace gas detection and thermography. However, current long-wave infrared spectro-polarimetric imagers are bulky and limited in terms of spectral resolution and field of view.
To overcome these limitations, researchers have turned to large-area metasurfaces, ultra-thin structured surfaces capable of manipulating light in complex ways. After designing rotating dispersive metasurfaces with suitable infrared responses, they developed a manufacturing process that made it possible to use these metasurfaces to create large surface rotating devices (2.5 cm in diameter) suitable for applications of imagery. The resulting rotating stack measures less than 10 x 10 x 10 cm and can be used with a traditional infrared camera.
“Integrating these large-area meta-optical devices with computational imaging algorithms has facilitated the efficient reconstruction of the thermal radiation spectrum,” Wang said. “This created a more compact, more robust and more efficient spectro-polarimetric thermal imaging system than was previously possible.”
The stack of rotating metasurfaces decomposes thermal light into its spectral and polarimetric components. The researchers combined the metasurface stack with a traditional long-wave infrared camera and computational imaging algorithms to create a compact and robust spectral thermal imaging system. Credit: Xueji Wang, Purdue University
Classification of materials by thermal imaging
To evaluate their new system, the researchers spelled out “Purdue” using various materials and microstructures, each with unique spectro-polarimetric properties. Thanks to the spectro-polarimetric information acquired with the system, they precisely distinguished the different materials and objects.
They also demonstrated a three-fold increase in material classification accuracy compared to traditional thermal imaging methods, highlighting the efficiency and versatility of the system.
The researchers say the new method could be particularly useful for applications requiring detailed thermal imaging. “In security, for example, it could revolutionize airport systems by detecting objects or substances concealed on people,” Wang said. “In addition, its compact and robust design improves its suitability for various environmental conditions, making it particularly advantageous for applications such as autonomous navigation.”
In addition to working on video capture with the system, researchers are trying to improve the technique’s spectral resolution, transmission efficiency, and speed of image capture and processing.
They also plan to improve the metasurface design to enable more complex manipulation of light for higher spectral resolution. Additionally, they want to extend the method to room temperature imaging, as using metasurface stacks limited the method to high-temperature objects. They plan to achieve this by using improved materials, metasurface designs, and techniques such as anti-reflective coatings.
More information:
Xueji Wang et al, Spinning Metasurface Stack for Spectro-polarimetric Thermal Imaging, Optical (2023). DOI: 10.1364/OPTICA.506813
Quote: Researchers use rotating metasurfaces to create compact thermal imaging system (January 11, 2024) retrieved January 11, 2024 from
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