Nanocrystals – Layered Metasurfaces For Infrared Imaging

Infrared imaging applications are growing from food quality control and remote sensing to night vision devices and LiDAR. IR cameras convert infrared light to electrons and project the resultant image on display. However, such cameras are bulky, disrupt normal vision, and require low temperatures. Alternatively, a nonlinear optical process – nonlinear sum-frequency generation (SFG) – can convert IR light into visible without any electrical signals. A human eye or phone-type camera can capture the image. Researchers used layers of ultrathin nanocrystals known as metasurfaces for IR to visible conversion.

Dielectric and semiconductor metasurfaces have shown great promise in enhancing nonlinear optical processes at the nanoscale. Such metasurfaces can exhibit enhanced frequency conversion due to the excitation of optical resonances and good coupling to free space.

The new nanocrystal approach can image IR objects through coherent conversion using ultrathin and ultralight devices. Transparent metasurfaces could perform IR imaging and transmit visible light to allow for normal vision.

Unlike current IR cameras, the all-optical approach is not affected by thermal noise and can operate at room temperature using conventional CMOS detectors. Importantly, the metasurface-based IR imaging approach provides opportunities not available in traditional upconversion systems that employ bulky nonlinear crystals. As long as the metasurface resonances are excited, nonlinear wave-mixing can be obtained for counterpropagating pump and signal beams, as well as incidence at all different angles. Most importantly, an appropriately designed metasurface allows for multicolor SWIR imaging.

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