Detection and characterization of an optical vortex by the branch point potential method: analytical and simulation results.

Singularities are discontinuities in optical wavefronts that can be produced by turbulence effects. Since the presence of singularities in a wavefront severely degrades the adaptive optics correction performance, their detection is very important. The gradient of the wavefront phase, as measured by the Shack-Hartmann wavefront sensor in the presence of singularities, can be considered as the sum of the rotational and irrotational parts. The rotational part of the phase gradient originating from the phase singularities can be considered as a potential based on Helmholtz-Hodge decomposition. The potential at the singularities positions appears as peaks and valleys of the potential depending on the positive or negative charges of singularities. In this article, the detection of phase singularities based on the branch point potential (BPP) method is investigated. The irrotational part of the gradient produces a background potential where singularities positions appear as local extremum of the potential. With our method, the irrotational part of the gradient is eliminated and the value of peaks and valleys is increased. In addition, in this method, the potential value characterizes the optical singularities. Here, analytical and simulation results for the detection of general forms of the singularity are presented. Our simulations show the performance of singularities detection in noisy conditions.

Reconstruction of two interfering wavefronts using Zernike polynomials and stochastic parallel gradient descent algorithm.

We numerically and experimentally demonstrate an iterative method to simultaneously reconstruct two unknown interfering wavefronts. A three-dimensional interference pattern is analyzed and then Zernike polynomials and the stochastic parallel gradient descent algorithm are used to expand and calculate wavefronts.

Application of the transport of intensity equation in determination of nonlinear refractive index.

We investigate the determination of nonlinear refractive index n(2), based on solving the transport of intensity equation (TIE) in conjunction with a pump-probe technique. As the pump and probe beams propagate through a sample, the pump-induced refractive index variations in the sample change the phase distribution of the probe beam. Using two recorded probe intensities in TIE, this phase change is derived, and so the nonlinear refractive index n(2) is obtained. The influence of some characteristics of the pump beam and noise on the accuracy of determining n(2) is also investigated. The simulation results show that the proposed method has a good capability for determining the nonlinear refractive index of materials.

Very low resistance ZnS/Ag/ZnS/Ag/ZnS nano-multilayer anode for organic light emitting diodes applications.

In this paper, design and simulation of conductive nanometric multilayer systems are discussed and optimum thickness of Ag and ZnS layers are calculated to reach simultaneously to high transmittance and low sheet resistance. The conductive transparent ZnS/Ag/ZnS/Ag/ZnS (ZAZAZ) nanometric multilayer systems are deposited on glass substrates at room temperature by a thermal evaporation method. The electrical, optical, and structural properties of these multilayers, such as sheet resistance, optical transmittance, and the root-mean-square surface roughness are obtained. High quality nanometric multilayer systems with sheet resistance of 2.7 Ω/sq and the optical transmittance of ~75.5% are obtained for the ZAZAZ system. Organic light emitting diodes (OLEDs) were fabricated and tested on the ZAZAZ anode. The ZAZAZ multilayer anode based OLED shows the performance comparable to that of the indium-tin oxide anode based OLED.