Nanohole-based phase gradient metasurfaces for light manipulation

The commonly accepted approach for metasurface design utilizes nanopillars with varying diameters. In this study, contrary to usual design approach, we propose and design highly efficient, broadband and polarization-independent nanohole all-dielectric metasurfaces operating in the visible spectrum. High focusing efficiency above 70% is achieved between 450 and 700 nm wavelength region with a numerical aperture (NA) value of 0.60. Moreover, focusing efficiency is succeeded higher than 47% with NA = 0.85 for a design wavelength of 532 nm. Nanohole metasurfaces exhibit less chromatic aberration (< 18%) compared to nanopillar based metasurfaces. The nanohole array metasurfaces is investigated under the oblique illumination condition and its performance is found to be satisfactory in a wide range of incidence angles. Furthermore, nanohole and nanopillar metasurfaces are analyzed and their performances are compared for different incidence angles, NAs and operating wavelengths. It is shown that contrary to dielectric pillars commonly deployed in the design of metasurfaces, nanoholes with varying diameters allow phase changes with better performances

Rotationally tunable polarization-insensitive single and multifocal metasurface

Metasurfaces with superior capabilities to tailor wave fronts of light have become one of the most widely investigated optical elements. Incorporating tunable features into the metasurface design is required. In this study, we have proposed and designed highly efficient rotationally tunable metasurface lens structures inspired by Moire lenses operating at a 532 nm wavelength. The proposed structures consist of two cascaded all-dielectric metasurfaces, which have reverse phase profiles with respect to each other. The metasurfaces are designed with periodically arranged TiO2 nano-rods on a SiO2 substrate in a square lattice. We demonstrated that the focal length changes nonlinearly according to the mutual rotation of metasurfaces from 30 degrees to 150 degrees with a focusing efficiency as high as 55% and a wide focal length variation between 11.4 mu m and 4.2 mu m. Moreover, we have designed and proposed a tunable polarization-insensitive multifunctional focal system. Using the proposed multifunctional focal system, focal planes can be formed in consecutive planes and the number of focal planes can be made single or multiple

Broadband asymmetric light transmission based on all-dielectric metasurfaces in the visible spectrum

An asymmetric transmission device composed of all dielectric phase gradient metasurfaces on the dielectric substrate in the visible wavelengths is proposed and designed. In order to verify its operation principle and investigate its asymmetric transmission performance, ray and wave analyses are employed together. Specifically, ray tracing and finite-difference time-domain techniques are carried out in the study. The analytical calculations of the designed structure are confirmed with the results of the ray and wave analysis. It is also demonstrated that broadband and high contrast asymmetric transmission occur across nearly the entire visible spectrum from wavelengths of 500-715 nm. Especially, the difference of transmission between forward and backward illuminations in the design wavelength of 532 nm is found to be nearly 90% under TM polarization. In addition, it is indicated that a slight degradation in the asymmetric transmission performance of the structure occurs due to the change of the light polarization. It is shown that the asymmetric transmission has been directly related to the total reflection of the light for only one direction excitation case. The proposed structure can be fabricated with emerging nanofabrication techniques in conformal metasurfaces and can be realized in different wavelength ranges

Accelerating beam generation via all-dielectric metasurfaces

Metamaterials XII (2019: Prague, Czech Republic )All-dielectric metasurfaces are unique component to control optical wavefront with high transmission or reflection coefficient. Recently, accelerating beam, which propagates along curved arbitrary trajectories, has been realized with conventional diffractive optical elements (DOE). However, DOE suffer from low sampling ratio of rapid phase gradients and its diffraction efficiency drops quickly when the wavelength is switched to another wavelength which is different than the designed wavelength. In this study, we show accelerating beam which is generated by highly efficient and polarization insensitive all-dielectric metasurfaces in the visible wavelength. The acceleration beam is numerically generated with the proposed metasurfaces which are composed of TiO2 nanopillars residing on glass substrate using finite difference time-domain computational method. It is shown that this beam has the ability to propagate curved trajectories in air medium. Transmission efficiency of the proposed structure is above 65% and desired arbitrary trajectories have been achieved. Generating highly efficient accelerating beam can be used in photonic applications in optical imaging, spectroscopy, optical micromanipulation and nonlinear optics. © 2019 SPIE

Tunable and asymmetric transmission of light in visible spectrum

Metamaterials XII (2019: Prague, Czech Republic )In modern optic and photonic applications, tunability of the asymmetric transmission has become important due to its adjustable unidirectional transmission. In this study, we design a three-dimensional trapezoidal metallic nano structure on a stretchable substrate. It shows broadband tunable asymmetric light transmission in the visible spectrum. The proposed structure is made of a periodic nano array of a trapezoidal shaped aluminum on a stretchable substrate. The transmission properties of the proposed structure with respect to the geometric parameters were systematically investigated employing finite-difference time-domain computations. It was shown that the intensity and the bandwidth of the asymmetric light transmission between 400 nm and 800 nm wavelengths change when the flexible substrate is stretched. The period of the designed structure varies depending on the stretch of the substrate. For example, when the substrate is stretched, the period of the structure is 450 nm and when it is unstretched, the period is 350 nm. This increase in the period causes a red shift in the wavelength range of the asymmetric transmission. While the asymmetric transmission under unstretched case starts at 350 nm and stops at 514.5 nm, under stretched case it starts at 450 nm and stops at 661.5 nm. In addition, the performance of our structure is insensitive the polarization of the incoming radiation in both forward and backward illumination directions. This study provides a path toward the realization of tunable optical devices for the applications which require dynamic tunability. © 2019 SPIE

Kinetics and equilibria of S-nitrosothiol—thiol exchange between glutathione, cysteine, penicillamines and serum albumin

AbstractThe kinetics and equilibria of S-nitrosothiol-thiol (SNO—SH) exchange reactions were determined using differential optical absorption. At pH 7.4 and 37°C, k2 values ranged from 0.9 M−1 · s−1 for the reaction between S-nitroso-glutathione (GSNO) and N-acetyl-penicillamine, and up to 279 M−1 · s−1 for the exchange between S-nitroso-penicillamine (penSNO) and GSH. SNO—SH exchange involving GSH/GSNO and cysteine/cySNO was relatively rapid, k2 approx. 80 M−1 · s−1 with an equilibrium constant slightly in favour of GSNO. GSNO was strongly favoured in equilibrium with penSNO, keq 0.0039. In the case of SNO—SH exchange between S-nitroso human serum albumin (albSNO) and GSH or cysteine k2 values were 3.2 and 9.1 M−1 · s−1, respectively. The results show that the initial rate of SNO—SH exchange between physiological albSNO (7 μM) and venous plasma levels of GSH and cysteine is very slow, < 1%/min. On the other hand, if a nitrosothiol such as cySNO were to enter a cell, it would be rapidly converted to GSNO (43%/s)

Serum amphiregulin and cerebellin-1 levels in severe preeclampsia

Purpose: Preeclampsia is a form of hypertensive disorders of pregnancy and defined as the presence of new-onset hypertension and proteinuria or other end organ damage occurring after 20-week gestation. Preeclampsia can be a destructive process that can cause maternal and infant mortality. The exact etiopathogenesis of preeclampsia is still undefined. We aimed to compare serum amphiregulin and cerebellin-1 levels of severe preeclampsia patients with healthy pregnant women and healthy control subjects. Materials and methods: A total of 88 women were enrolled in this study. Patients diagnosed with severe preeclampsia were group 1 (n?=?28), healthy non-pregnant normotensive women group 2 (n?=?30), and healthy pregnant women group 3 (n?=?30). The participants in each group were matched for age. Pregnant women in groups 1 and 3 were also matched for gestational age. Serum amphiregulin and cerebellin-1 levels were measured using ELISA. Results: Serum amphiregulin levels were 3413???1.38?ng/ml (1748?7739), 8510???7213?ng/ml (2019?24,000), and 6580???5360?ng/ml (2484?24,000) in preeclampsia patients, controls and healthy pregnant women, respectively. Amphiregulin levels were significantly lower in preeclampsia patients than healthy pregnant women (p=.008) and controls (p?=?.015). Amphiregulin levels were similar between healthy controls and healthy pregnant women (p??=??1.00). Cerebellin-1 levels were 222.039???92.681?pg/ml (138,580?557,757) in preeclamptic patients, 537.043???525.117?pg/ml (150,432?1,600,000) in controls and 415.091???436.580?pg/ml (137,284?1,600,000) in healthy pregnant women. Cerebellin-1 levels were similar among groups (p?=?.272). Serum amphiregulin and cerebellin-1 levels were significantly and positively correlated with each other in preeclampsia patients (r??=??0.693, p?<?.001), controls (r??=??0.882, p?<?.001), and healthy pregnant women (r??=??0.591, p?=?.001). Serum level of amphiregulin ?3590?pg/ml had a sensitivity of 67.9% and specificity of 63.3% in the diagnosis of preeclampsia (AUC: 0.751; p?=?.001). Conclusions: Serum amphiregulin decreases in severe preeclampsia patients