Arbitrary-order lensless ghost imaging with thermal light

Arbitrary Nth-order ($N\geq2$) lensless ghost imaging with thermal light has been performed for the first time by only recording the intensities in two optical paths. It is shown that the image visibility can be dramatically enhanced as the order N increases. It is also found that longer integration times are required for higher-order correlation measurements as N increases, due to the increased fluctuations of higher-order intensity correlation functions.Comment: Updated version; some more detailed explanations provide

Planar holographic metasurfaces for terahertz focusing.

Scientists and laymen alike have always been fascinated by the ability of lenses and mirrors to control light. Now, with the advent of metamaterials and their two-dimensional counterpart metasurfaces, such components can be miniaturized and designed with additional functionalities, holding promise for system integration. To demonstrate this potential, here ultrathin reflection metasurfaces (also called metamirrors) designed for focusing terahertz radiation into a single spot and four spaced spots are proposed and experimentally investigated at the frequency of 0.35 THz. Each metasurface is designed using a computer-generated spatial distribution of the reflection phase. The phase variation within 360 deg is achieved via a topological morphing of the metasurface pattern from metallic patches to U-shaped and split-ring resonator elements, whose spectral response is derived from full-wave electromagnetic simulations. The proposed approach demonstrates a high-performance solution for creating low-cost and lightweight beam-shaping and beam-focusing devices for the terahertz band.This work was supported by the Ministry of Education and Science of the Russian Federation under the State Assignment Contract #3002 (implementation of the Gerchberg-Saxton iterative algorithm and experimental testing), the Russian Science Foundation under the Project 14-12-01037 (full-wave electromagnetic simulations), and the Spanish Government under contracts Consolider “Engineering Metamaterials” CSD2008-00066, and TEC2011-28664-C01. M. Beruete acknowledges funding by the Spanish Government under the research contract program Ramón y Cajal RYC-2011-08221. M. N.-C. was supported by Imperial College London through a Junior Research Fellowship