Researchers have created a new technique for thermal imaging using meta-optical devices. This approach provides more detailed information about the object being imaged, potentially expanding the applications of thermal imaging in autonomous navigation, security, thermal imaging, medical imaging, and remote sensing.
"Our method overcomes the challenges of traditional spectral thermal imagers, which are often bulky and sophisticated because they rely on large filter wheels or interferometers," said research team leader Zubin Jacob from Purdue University. "We combined meta-optical equipment and cutting-edge computational imaging algorithms to create a system that is both compact and robust, while also having a large field of view."
In Optica, the high-impact research journal of Optics Publishing Group, the authors describe their new spectral polarization decomposition system, which uses a stack of rotating element surfaces to decompose thermal light into its spectral and polarization components. In this way, the imaging system can capture the spectral and polarization details of the thermal radiation in addition to the intensity information acquired by traditional thermal imaging techniques.
The researchers' study shows that the new system can be used with commercial thermal imaging cameras to successfully classify a variety of materials, which is often a challenging task for traditional thermal imaging cameras. This method can distinguish temperature changes and identify materials based on spectral polarization signatures, helping to improve safety and efficiency in a variety of applications, including autonomous navigation.
Xueji Wang, the first author of this article and a postdoctoral researcher at Purdue University, said: "Traditional autonomous navigation methods mainly rely on RGB cameras, which are difficult to function in harsh conditions such as low light or bad weather. Combined with thermal-assisted detection and ranging technology, our spectral polarization thermal imaging camera can provide important information in these difficult situations, providing clearer images than RGB or traditional thermal imaging cameras. Once we achieve real-time video capture, this technology can greatly improve scene perception and overall safety."
Do more with a smaller camera
Longwave infrared spectroscopy polarization imaging is critical for applications such as night vision, machine vision, trace gas sensing, and thermal imaging. However, today's spectral polar longwave infrared imagers are bulky and have limited spectral resolution and field of view.
To overcome these limitations, researchers are turning to large-area element surfaces—ultrathin structured surfaces that can manipulate light in complex ways. After designing rotating dispersive metasurfaces with tailored infrared responses, they developed a fabrication process that can use these metasurfaces to create large-area (2.5 cm diameter) rotating devices suitable for imaging applications. The resulting rotating stack measures less than 10x10x10 cm and can be used with traditional infrared cameras.
"Combining these large-area element optical devices with computational imaging algorithms helps to efficiently reconstruct thermal radiation spectra. This makes spectral polar thermal imaging systems more compact, robust and efficient than previous systems."
Using thermal imaging to classify materials
To evaluate their new system, the researchers spelled out "Purdue University" using a variety of materials and microstructures, each with unique spectral polar properties. Using the spectral polar coordinate information acquired by the system, they accurately distinguished between different materials and objects. They also demonstrated that the system's material classification accuracy was three times higher compared to traditional thermal imaging methods, highlighting the system's effectiveness and versatility.
The researchers say the new method will be particularly useful for applications requiring detailed thermal imaging. "For example, in the security field, it can revolutionize airport systems by detecting items or substances hidden on people," Wang Xueji said. "In addition, its compact and sturdy design enhances its applicability in different environmental conditions, making it particularly beneficial for applications such as autonomous navigation."
In addition to utilizing the system for video capture, the researchers are also working to improve the technology's spectral resolution, transmission efficiency, and image capture and processing speed. They also plan to improve the metasurface design to enable more complex light manipulation, resulting in higher spectral resolution. Additionally, they hope to extend the method to room-temperature imaging, since the use of metasurface stacks limits the method's application to high-temperature objects. They plan to use technologies such as improved materials, meta-surface design and anti-reflective coatings to achieve this goal.
Compiled from /ScitechDaily