visible-to microwave-frequencies, [3][4][5][6] however, with rather small operation bandwidths. Likewise, 3D chiral dielectric photonic crystals [7][8][9][10][11] also show fairly small operation bandwidths.In sharp contrast, metallic helical metamaterials exhibit circular dichroism over an unmatched bandwidth of well above one octave. Starting with square arrays of single gold helices that function as broadband circular polarizers with high extinction ratio in the mid infrared, [ 12,13 ] recently research has led to more complex unit cells. For example, by tapering the helix radius along the helix axis, the extinction ratio and the bandwidth can be enhanced simultaneously. [ 14 ] Double-helical unit cells have also been proposed to lead to higher extinction ratios and enlarged bandwidths. [15][16][17][18] Circular polarization conversions are often unwanted for polarizer applications. They can be eliminated by recovering either threefold or fourfold rotational symmetry by intertwining three or four helices, respectively, within one unit cell of a lattice with the same rotational symmetry. [19][20][21][22][23] Applications beyond circular polarizers such as broadband absorbers [ 24 ] or chiral near-fi eld sources [ 25 ] have also been proposed.While for circular polarizers a large difference of the diagonal elements of the Jones transmission matrix is desired, chiral metamaterials can also be designed to exhibit strong circular polarization conversions corresponding to the off-diagonal elements. Even though converting one circular polarization to the other can be achieved by half-wave plates at visible frequencies, these wave plates are often limited in bandwidth and not readily available at many other frequency ranges.Furthermore, a large difference in these off-diagonal elements can be of interest, both in linear and circular polarization basis. This effect is often referred to as "asymmetric transmission" due to the symmetry of the Jones transmission matrix. Applications like diode-like devices exploiting asymmetric Jones matrices have been proposed. [ 26 ] Metamaterial designs with highly asymmetric polarization conversions have been realized for linearly polarized light, both at infrared-and terahertz-frequencies. [ 27,28 ] More recently, many more designs for linearly polarized light have been proposed with both high extinction ratios and large bandwidths. [29][30][31][32][33] Asymmetric polarization conversions for circular polarization, on the other hand, has only been reported recently, however, with generally much Metallic helical metamaterials give rise to broadband and scalable chirooptical effects orders of magnitude higher than found in nature. While arrays of gold helices have been suggested as compact circular polarizers, where a large difference of the diagonal elements of the Jones transmission matrix is desired, chiral metamaterials can also be designed to exhibit strong circularpolarization conversions. Here, a novel helical metamaterial design, exhibiting asymmetric, broadband circular-polari...

The spin and orbital angular momentum (SAM and OAM) of light is providing a new gateway toward high capacity and robust optical communications. While the generation of light with angular momentum is well studied in linear optics, its further integration into nonlinear optical devices will open new avenues for increasing the capacity of optical communications through additional information channels at new frequencies. However, it has been challenging to manipulate the both SAM and OAM of nonlinear signals in harmonic generation processes with conventional nonlinear materials. Here, we report the generation of spin-controlled OAM of light in harmonic generations by using ultrathin photonic metasurfaces. The spin manipulation of OAM mode of harmonic waves is experimentally verified by using second harmonic generation (SHG) from gold meta-atom with 3-fold rotational symmetry. By introducing nonlinear phase singularity into the metasurface devices, we successfully generate and measure the topological charges of spin-controlled OAM mode of SHG through an on-chip metasurface interferometer. The nonlinear photonic metasurface proposed in this work not only opens new avenues for manipulating the OAM of nonlinear optical signals but also benefits the understanding of the nonlinear spin-orbit interaction of light in nanoscale devices.

The average valence, ValO, of the oxygen anions in the perovskite oxide BaTiO3, was found using O1s photoelectron spectra to be −1.55. This experimental result is close to the theoretical value for BaTiO3 (−1.63) calculated by Cohen [Nature 358, 136 (1992)] using density functional theory. Using the same approach, we obtained values of ValO for several monoxides, and investigated the dependence of ValO and the ionicity on the second ionization energy, V(M2+), of the metal cation. We found that the dependence of the ionicity on V(M2+) in this work is close to that reported by Phillips [Rev. Mod. Phys. 42, 317 (1970)]. We therefore suggest that O1s photoelectron spectrum measurements should be accepted as a general experimental method for estimating the ionicity and average valence of oxygen anions.

The H. pylori infection rate in Asian IBD patients is significantly lower than in non-IBD patients, indicating that infection protects against the development of IBD.