New high-resolution laser device reads millimeter-scale text from a mile away

You are the protagonist in a thriller. One morning, an unknown caller with a distorted voice says, “To save your city, solve the puzzle. Go to the coordinates. X marks the clue.” You rush to the spot and see an X on a distant billboard, too far to read. Your vision is sharp, but not that sharp. So, what do you do? A new laser emitter designed by a team of researchers from China could come to the rescue.

According to the study published in Physical Review Letters, the developed setup includes multiple laser emitters that enable super-resolution imaging of targets as small as millimeters in scale from a 1.36 kilometers (0.85 miles) distance in an outdoor urban environment. The device successfully images letter-shaped physical targets measuring 8×9 mm, with letter widths of 1.5 mm, placed at the far end of its imaging range.

Interferometry is a widely used imaging technique in astronomy which works by merging light from different sources to create an interference pattern. These interference patterns are formed when light waves interact to either reinforce or cancel each other depending on their phase differences. These patterns carry detailed information about the object or phenomenon being studied.

Intensity interferometry, on the other hand, does not rely on combining light amplitudes or maintaining phase information but on light from a single source being measured separately by two detectors or telescopes, and the variations in their recorded intensities are compared.

Studying intensity fluctuations, correlations and their changes with the distance between the detectors can help extract spatial details about the object being studied.

What makes intensity interferometry stand out? It can cut through atmospheric turbulence and ignore flaws in telescope optics—making it ideal for long-distance, high-resolution imaging. Yet, its applications have mostly been limited to observing bright stars or objects that can be lit up with nearby light sources.

Scientists have attempted to expand its scope to active imaging applications such as light detection and ranging or LiDAR, but the lack of suitable thermal light sources and robust image reconstruction algorithms make the process challenging.

To overcome these issues, the researchers created an intensity interferometer setup with pseudothermal illumination achieved by superimposing light from 8-phase-independent multiple laser emitters. This setup included two telescopes and an infrared laser system on a shared optical bench.

The laser system produced thermal illumination, and reconstructed sparse, noisy data being collected into a high-resolution image with the help of a computational algorithm.

To test the super-resolution capabilities of the device, the letters “USTC” were crafted out of hollowed-out blackened aluminum sheets which were then covered in retroreflective sheets and used as a complex imaging target positioned over a kilometer away.

Using the designed active intensity interferometer, the researchers successfully demonstrated super-resolution imaging of millimeter-scale targets at a distance of 1.36 km in an outdoor urban environment. The imaging system achieved a resolution of 3 mm, which is 14 times higher than the diffraction limit of a single telescope, typically around 42.5 mm.

Once scaled for use beyond the laboratory, this device could significantly accelerate advancements in long-range, high-resolution remote sensing, surveillance, and non-invasive imaging in challenging environments.

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