Imagine being able to snap a picture of extremely fast events on the order of a picosecond. Compressed ultrafast photography (CUP) captures the entire process in real time and unparalleled resolution with just one click. The spatial and temporal information is first compressed into an image and then, using a reconstruction algorithm, it is converted into a video.

Until now, this technique was limited to visible and near-infrared wavelengths, and thus to a specific category of physical events. “Many phenomena that occur on very short time scales also take place on a very small spatial scale. To see them, you need to sense shorter wavelengths. Doing this in the UV or even X-ray ranges is a remarkable step toward this goal,” said Professor Jinyang Liang.

Compact, one-box UV-CUP system. (Credit: Jinyang Liang)

To record in this new range of wavelengths and to develop the technique into a user-friendly product, researchers designed a compact UV-CUP system with Axis Photonique, Inc. via an academia-industry collaboration. The new system features a patterned photocathode, which is used to simultaneously detect and encode “black light.” “Like a standard camera, our technology is passive. It does not produce light; it receives it. Therefore, our photocathode had to be sensitive to the photons emitted as UV light. This design makes our technique a stand-alone system that can be easily integrated into various experimental platforms,” said Liang.

Taking the picture is only the first half of the job — it also has to be reconstructed. To do this, the researchers developed a new algorithm, more efficient than standard algorithms, via their collaboration with Boston University. Its strength comes from a division of tasks. Rather than solve the reconstruction problem as a lump, the algorithm divides the reconstruction into smaller problems that it tackles individually.

With the innovations in both hardware and software, UV-CUP has an imaging speed of 0.5 trillion frames per second. It produces videos with 1500 frames in large format. As a light-speed imager, UV-CUP sees flying UV photons in real time.

Even though it is the fastest camera in the world, the device can still be improved. For example, the chosen photocathodes have limited efficiency, so researchers want to explore other types of materials. Regarding reconstruction, Liang says that the algorithm has greatly improved the quality, but that it still takes quite a long time. To increase its speed, he is collaborating with Professor Tiago Falk, also from INRS, on using artificial intelligence to improve it.

The device developed through this international collaboration will be sent to the research laboratory SOLEIL Synchrotron in France to visualize physical phenomena. It could capture laser-plasma generation, a phenomenon that is essential for deducing certain properties of materials, and UV fluorescence, which is important in medical imaging to identify biomarkers linked to diseases.

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Photonics & Imaging Technology Magazine

This article first appeared in the March, 2021 issue of Photonics & Imaging Technology Magazine.

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