&Cartridge; physics 14, s97

An update to a technique for imaging around corners allows researchers to capture out-of-sight objects that are a few human hairs wide, 100 times smaller than previous demonstrations.

Seeing around corners without a mirror may seem impossible, but there are methods that researchers can use to get an approximate image of flare in such situations. So far, these so-called non-line-of-sight (NLOS) techniques had a spatial resolution of a few centimeters. By modifying such a method, a team of researchers in China has achieved a 100-fold improvement in this resolution and enables them to image features with a diameter of a few hundred micrometers [1] .

NLOS methods map hidden objects by capturing photons that travel indirectly from the object to a detector. These photons can be scattered from multiple surfaces before landing on the NLOS setup. Each scattering path has a different length, which leads to a scattering of the arrival times of the photons at the detector: A difference in length of a few hundred micrometers corresponds to a picosecond difference in the arrival times of the photons. Since the maximum temporal resolution of previous photon detectors was a few tens of picoseconds, their spatial resolution was limited to a few centimeters.

During their construction, Bin Wang from the University of Science and Technology of China and colleagues replaced the standard photon detector with a laser-pumped “up-conversion” photon detector. The laser pump enabled them to carefully select the photons registered on the detector and to determine the arrival times of the incoming photons more precisely. These two factors helped improve the time resolution of the detector to a picosecond. The team demonstrated the effect of this improvement by using their improved setup to display millimeter-high letters hidden behind a wall. The resulting images have an axial resolution of 180 [TeX:] $ mu textrm {m} $ and a lateral resolution of 2 mm.

–Katherine Wright

Katherine Wright is assistant editor of physics.


  1. B. Wang et al., “Imaging without line of sight with temporal resolution of picoseconds”, Phys. Rev. Lett.127, 053602 (2021).

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