Researchers from the University of Central Florida (UCF) have developed a specialized tunable detection and imaging technique for infrared photons that reportedly surpasses present technology and may be a cost-effective method of capturing thermal imaging or night vision, medical imaging, spectroscopy and space exploration.
The new technique detects long wave infrared (LWIR) photons of different wavelengths or “colors”. It was reported that these findings are the result of a $1.5 million project funded through the Extreme Photon Imaging Capabilities program of the Defense Advanced Research Projects Agency that was awarded nearly two years ago.
The new detection and imaging technique could have applications in analyzing materials by their spectral properties, or spectroscopic imaging, as well as thermal imaging applications.
Humans perceive primary and secondary colors but not infrared light. Scientists hypothesize that animals like snakes or nocturnal species can detect various wavelengths in the infrared almost like how humans perceive colors. Infrared, specifically LWIR, detection at room temperature has been a long-standing challenge due to the weak photon energy.
LWIR detectors can be broadly classified into either cooled or uncooled detectors, the UCF team says. Cooled detectors excel in high detectivity and fast response times but their reliance on cryogenic cooling significantly escalates their cost and restricts their practical applications. In contrast, uncooled detectors, like microbolometers, can function at room temperature and come at a relatively lower cost but exhibit lower sensitivity and slower response times.
Both kinds of LWIR detectors lack the dynamic spectral tunability, and so they can’t distinguish photon wavelengths of different “colors.”
UCF Professor Debashis Chanda and his team of postdoctoral scholars sought to expand beyond the limitations of existing LWIR detectors, so they worked to demonstrate a highly sensitive, efficient and dynamically tunable method based on a nanopatterned graphene.
“No present cooled or uncooled detectors offer such dynamic spectral tunability and ultrafast response,” Chanda says. “This demonstration underscores the potential of engineered monolayer graphene LWIR detectors operating at room temperature, offering high sensitivity as well as dynamic spectral tunability for spectroscopic imaging.”
The detector relies on a temperature difference in materials (known as the Seebeck effect) within an asymmetrically patterned graphene film. Upon light illumination and interaction, the patterned half generates hot carriers with greatly enhanced absorption while the unpatterned half remains cool. The diffusion of the hot carriers creates a photo-thermoelectric voltage and is measured between the source and drain electrodes.
By patterning the graphene into a specialized array, the researchers achieved an enhanced absorption and can further electrostatically tune within the LWIR spectra range and provide better infrared detection. The detector significantly surpasses the capabilities of the conventional uncooled infrared detectors — also known as microbolometers.
“The proposed detection platform paves the path for a new generation of uncooled graphene-based LWIR photodetectors for wide ranging applications such as consumer electronics, molecular sensing and space to name a few,” Chanda says.