High efficiency dielectric metasurfaces at visible wavelengths
  Metasurfaces are planar optical elements that hold promise for overcoming the limitations of refractive and conventional diffractive optics1-3. Dielectric metasurfaces demonstrated thus far4-10 are limited to transparency windows at infrared wavelengths because of significant optical absorption and loss at visible wavelengths. It is critical that new materials and fabrication techniques be developed for dielectric metasurfaces at visible wavelengths to enable applications such as three-dimensional displays, wearable optics and planar optical systems11. Here, we demonstrate high performance titanium dioxide dielectric metasurfaces in the form of holograms for red, green and blue wavelengths with record absolute efficiency (>78%). We use atomic layer deposition of amorphous titanium dioxide that exhibits low surface roughness of 0.738 nm and ideal optical properties. To fabricate the metasurfaces we use a lift-off-like process that allows us to produce highly anisotropic nanofins with shape birefringence. This process is applicable to any optical element and can be implemented using a broad class of materials. 
Robert C. Devlin, Mohammadreza Khorasaninejad, Wei-Ting Chen, Jaewon   Oh and Federico Capasso
physics.optics