Transport of intensity and phase: applications to digital holography [Invited].

We first review transport of intensity and phase and show their use as a convenient tool to directly determine the unwrapped phase of an imaged object, either through conventional imaging or using digital holography. For both cases, either the traditional transport of intensity and phase, or with a modification, viz., electrically controllable transport of intensity and phase, can be used. The use of digital holography with transport of intensity for 3D topographic mapping of fingermarks coated with columnar thin films is shown as an illustrative application of this versatile technique.

Noise analysis of Grover and phase estimation algorithms implemented as quantum singular value transformations for a small number of noisy qubits.

The quantum singular value transformation (QSVT) algorithm is a general framework to implement most of the known algorithms and provides a way forward for designing new algorithms. In the present work, the impact of noise on the QSVT algorithm is examined for bit flip, phase flip, bit-phase flip, and depolarizing noise models for a small number of qubits. The small number of noisy qubits approximates the currently available noisy quantum computers. For simulation results, the QSVT implementation of the Grover search and quantum phase estimation (QPE) algorithms is considered. These algorithms are among the basic quantum algorithms and form the building blocks of various applications of quantum algorithms. The results showed that the QSVT implementation of the Grover search and QPE algorithms has a consistently worse dependence upon noise than the original implementation for all four noise models. The probability of success of the Grover algorithm and phase measured by the QPE algorithm were found to exponentially depend upon the error probability in the noisy channels but only linearly dependent on the number of qubits.

Therapeutic Potential of Selected Varieties of Phoenix Dactylifera L. Against Microbial Biofilm and Free Radical Damage to DNA.

Phoenix dactylifera L. (Date palm) is the most widely consumed fruit around the world and is rich source of nutrients containing dietary fibers, minerals, vitamins, sugar, protein and antioxidants with potent bioactivities against various microbial pathogens. This study evaluated the therapeutic potential of 2 varieties of ethanolic extracts of Phoenix dactylifera i-e Ajwa and Khalas against bacterial biofilms. This study also investigated the protective effect of Ajwa and Khalas against hydroxyl radical damage to calf thymus DNA. Antioxidant potential through different antioxidant assays showed that Ajwa has higher antioxidant potential than Khalas. Both Ajwa and Khalas presented good antimicrobial activities against Bacillus subtilis and Pasteurella multocida. Biofilm inhibition assay showed that increasing concentration of Ajwa and Khalas exhibited higher percentage of bacterial biofilm inhibition. Microscopic examination revealed significant inhibition of microbial biofilm. Ajwa and Khalas protected the calf thymus DNA against damage caused by hydroxyl radicals produced by fenton reagent. Fourier Transform Infrared (FTIR) spectra confirmed the presence of O-H, C=C and C-O functional groups in tested extracts. The study concluded that tested varieties of Date palm have the potential to inhibit bacterial biofilms and can be used for therapeutic purposes against biofilm producing pathogens.

Adequacy of the rigorous coupled-wave approach for thin-film silicon solar cells with periodically corrugated metallic backreflectors: spectral analysis.

The rigorous coupled-wave approach (RCWA) is extensively used to compute optical absorption and photon absorption in thin-film photovoltaic solar cells backed by 1D metallic gratings when the wave vector of the incident light lies wholly in the grating plane. The RCWA algorithm converges rapidly for incident s-polarized light over the entire 400-1100 nm solar spectrum. It also performs well for incident p-polarized light in the 400-650 nm spectral regime, but even with a large number of Floquet harmonics in the solution, the total reflectance is underestimated in the 650-1100 nm spectral regime. Despite that shortcoming, the RCWA underestimates the solar-spectrum-integrated photon absorption rate only by 5%-10% for p-polarized light. As sunlight is almost unpolarized, the RCWA should be considered adequate to design thin-film silicon solar cells with periodically corrugated metallic backreflectors.

Comparison of rigorous coupled-wave approach and finite element method for photovoltaic devices with periodically corrugated metallic backreflector.

Optimal design of photovoltaic devices with a periodically corrugated metallic backreflector requires a rapid and reliable way to simulate the optical characteristics for wide ranges of wavelengths and angles of incidence. Two independent numerical techniques are needed for confidence in numerical results. We compared the rigorous coupled-wave approach (RCWA) and the finite element method (FEM), the former being fast and flexible, but the latter having predictable convergence even for discontinuous constitutive properties. Depending on the shape of the corrugation and the constitutive properties of the metal and dielectric materials making up the device, both techniques can exhibit slow convergence rates for p-polarized light. The chosen model problem in this paper is of this type. As rapid spatial variations of the fields are the underlying cause, suitable selective refinement of the FEM mesh can overcome this slow convergence. Therefore, it would be desirable to have a self-adaptive scheme for choosing the mesh in the FEM. This will slow down the algorithm but give a reliable way to check the RCWA results.

Observation of the Uller-Zenneck wave.

The Uller-Zenneck wave has been theoretically predicted to exist at the planar interface of two homogeneous dielectric materials of which only one must be dissipative. Experimental confirmation of this century-old prediction was obtained experimentally by exciting the Uller-Zenneck wave as a Floquet harmonic of nonzero order at the periodically corrugated interface of air and crystalline silicon in the 400-to-900-nm spectral regime. Application for intrachip optical interconnects at 850 nm appears promising.

Experimental excitation of the Dyakonov-Tamm wave in the grating-coupled configuration.

The Dyakonov-Tamm wave was experimentally excited along the periodically corrugated interface of magnesium fluoride as the isotropic homogeneous partnering material and a zinc-selenide chiral sculptured thin film (STF) as the anisotropic and periodically nonhomogeneous partnering material. The total transmittance of a p-polarized 633 nm laser beam was measured as a function of the angle of incidence for several thicknesses of the chiral STF to identify those dips in total transmittance that are indicative of the excitation of a Dyakonov-Tamm wave.

Broadband light absorption with multiple surface plasmon polariton waves excited at the interface of a metallic grating and photonic crystal.

Light incident upon a periodically corrugated metal/dielectric interface can generate surface plasmon polariton (SPP) waves. This effect is used in many sensing applications. Similar metallodielectric nanostructures are used for light trapping in solar cells, but the gains are modest because SPP waves can be excited only at specific angles and with one linear polarization state of incident light. Here we report the optical absorptance of a metallic grating coupled to silicon oxide/oxynitride layers with a periodically varying refractive index, i.e., a 1D photonic crystal. These structures show a dramatic enhancement relative to those employing a homogeneous dielectric material. Multiple SPP waves can be activated, and both s- and p-polarized incident light can be efficiently trapped. Many SPP modes are weakly bound and display field enhancements that extend throughout the dielectric layers. These modes have significantly longer propagation lengths than the single SPP modes excited at the interface of a metallic grating and a uniform dielectric. These results suggest that metallic gratings coupled to photonic crystals could have utility for light trapping in photovoltaics, sensing, and other applications.

Specific biomimetic hydroxyapatite nanotopographies enhance osteoblastic differentiation and bone graft osteointegration.

Impaired healing of cortical bone grafts represents a significant clinical problem. Cadaveric bone grafts undergo extensive chemical processing to decrease the risk of disease transmission; however, these processing techniques alter the bone surface and decrease the osteogenic potential of cells at the healing site. Extensive work has been done to optimize the surface of bone grafts, and hydroxyapatite (HAP) and nanotopography both increase osteoblastic differentiation. HAP is the main mineral component of bone and can enhance osteoblastic differentiation and bone implant healing in vivo, while nanotopography can enhance osteoblastic differentiation, adhesion, and proliferation. This is the first study to test the combined effects of HAP and nanotopographies on bone graft healing. With the goal of identifying the optimized surface features to improve bone graft healing, we tested the hypothesis that HAP-based nanotopographic resurfacing of bone grafts improves integration of cortical bone grafts by enhancing osteoblastic differentiation. Here we show that osteoblastic cells cultured on processed bones coated with specific-scale (50-60 nm) HAP nanotopographies display increased osteoblastic differentiation compared to cells on uncoated bone, bones coated with poly-l-lactic acid nanotopographies, or other HAP nanotopographies. Further, bone grafts coated with 50-60-nm HAP exhibited increased formation of new bone and improved healing, with mechanical properties equivalent to live autografts. These data indicate the potential for specific HAP nanotopographies to not only increase osteoblastic differentiation but also improve bone graft incorporation, which could significantly increase patient quality of life after traumatic bone injuries or resection of an osteosarcoma.

Optimization of the absorption efficiency of an amorphous-silicon thin-film tandem solar cell backed by a metallic surface-relief grating.

The rigorous coupled-wave approach was used to compute the plane-wave absorptance of a thin-film tandem solar cell with a metallic surface-relief grating as its back reflector. The absorptance is a function of the angle of incidence and the polarization state of incident light; the free-space wavelength; and the period, duty cycle, the corrugation height, and the shape of the unit cell of the surface-relief grating. The solar cell was assumed to be made of hydrogenated amorphous-silicon alloys and the back reflector of bulk aluminum. The incidence and the grating planes were taken to be identical. The AM1.5 solar irradiance spectrum was used for computations in the 400-1100 nm wavelength range. Inspection of parametric plots of the solar-spectrum-integrated (SSI) absorption efficiency and numerical optimization using the differential evolution algorithm were employed to determine the optimal surface-relief grating. For direct insolation, the SSI absorption efficiency is maximizable by appropriate choices of the period, the duty cycle, and the corrugation height, regardless of the shape of the corrugation in each unit cell of the grating. A similar conclusion also holds for diffuse insolation, but the maximum efficiency for diffuse insolation is about 20% smaller than for direct insolation. Although a tin-doped indium-oxide layer at the front and an aluminum-doped zinc-oxide layer between the semiconductor material and the backing metallic layer change the optimal depth of the periodic corrugations, the optimal period of the corrugations does not significantly change.

Observation of the Dyakonov-Tamm wave.

A surface electromagnetic wave called the Dyakonov-Tamm wave has been theoretically predicted to exist at the interface of two dielectric materials at least one of which is both anisotropic and periodically nonhomogeneous. For experimental confirmation, a prism-coupled configuration was used to excite Dyakonov-Tamm waves guided by the interface of a dense thin film of magnesium fluoride and a chiral sculptured thin film of zinc selenide. The excitation was indicated by a reflection dip (with respect to the angle of incidence in the prism-coupled configuration) that is independent of the polarization state of the incident light as well as the thicknesses of both partnering materials beyond some thresholds. Applications to optical sensing and long-range on-chip communication are expected.