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 a display. However, such cameras are bulky, disrupt normal vision, and require low temperature. 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 to enhance 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 nanocrystals 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.