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Low-Cost Terahertz Camera in the U.S.

Image credits: news.mit.edu

Between the wavelengths of microwaves and visible light, terahertz radiation can penetrate various nonmetallic materials and identify chemical fingerprints. These convenient features could be used for a variety of tasks, such as airport security screening, quality control in the workplace, astronomical observations, nondestructive material characterisation, and wireless communications with higher bandwidth than current mobile bands.

Most terahertz devices currently in use, however, are pricy, sluggish, large, require vacuum systems, and operate at extremely low temperatures, making it difficult to develop devices that detect and create images from terahertz waves.

With this, a new type of camera that can quickly, highly sensitively, and at room temperature and pressure detect terahertz pulses has now been created by researchers from the Massachusetts Institute of Technology (MIT), the University of Minnesota, and a commercial mobile company.

Additionally, unlike prior devices, it can simultaneously record data regarding the waves’ orientation, or “polarisation,” in real-time. Asymmetrical molecule-containing materials can be identified, or their surface topography can be ascertained using this knowledge.

Quantum dots, which are used in the new technology, have recently been discovered to be able to emit visible light when activated by terahertz vibrations. Then, the visible light can be seen with the naked eye and collected by a gadget that looks like a standard electronic camera’s detector.

The group created two distinct devices that can work at room temperature: one makes use of the quantum dot’s capacity to transform terahertz pulses into visible light, enabling the device to produce images of materials; the other generates images revealing the polarisation state of the terahertz waves.

The new “camera” is made up of several layers and was created using industry-standard manufacturing processes like those for microchips. A layer of light-emitting quantum dot material is applied to the substrate, followed by a coating of gold nanoscale parallel lines divided by small slits, and ultimately, an image is created using a CMOS chip.

A polarimeter, which has a construction like that of the polarisation detector, can detect the polarisation of incoming beams by using ring-shaped nanoscale slits. The sensitivity and resolution of the detector were proved by the researchers by taking terahertz-illuminated photographs of some of the structures utilised in their devices, such as the nano-spaced gold lines and the ring-shaped slits used for the polarised detector.

A component that generates terahertz waves to illuminate a subject and another that detects them are needed to build a viable terahertz camera. Regarding the latter, modern terahertz detectors either use photodetectors, which are reasonably quick but have extremely limited sensitivity, and are therefore very slow because they rely on sensing heat generated by the waves striking a substance, and heat propagates slowly. Additionally, up until now, most techniques required many terahertz detectors, each of which produced one pixel of the image.

The dearth of high-quality sources still exists, even though the researchers claim to have solved the terahertz pulse detection problem with their current study which is being addressed by numerous research organisations across the globe.

Recent sources-based microelectronic techniques are actively being developed, but the terahertz source employed in the new work is a huge and heavy array of lasers and optical devices that cannot simply be scaled to practical uses.

The researchers claim that there are other methods to increase the sensitivity of the new camera, including additional component downsising and strategies for safeguarding the quantum dots. The device may still have some uses even at the current detection levels.

Regarding the new device’s commercialisation potential, those quantum dots are currently accessible and affordable, and they are employed in consumer goods like television displays. Although the actual manufacturing of the camera devices is more difficult, it still relies on current microelectronics technology.

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