Publications by authors named "Hamid R Fallah"
We numerically demonstrate a novel method to simultaneously reconstruct two unknown interfering wavefronts. The speckle-based phase retrieval technique is applied to derive the interference field. The derived interference field along with the phase-shifting concept is used for calculating the interfering wavefronts.
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- Singularities in optical wavefronts can lead to degraded performance in adaptive optics due to turbulence effects, making their detection crucial.
- The gradient of the wavefront phase is split into rotational and irrotational components, with singularities represented as peaks and valleys in the phase gradient's potential using a Helmholtz-Hodge decomposition.
- This article explores a method called branch point potential (BPP) for detecting phase singularities, where the irrotational part is eliminated to emphasize the singularities and improve detection performance, even in noisy conditions.
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.
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- Developed an iterative method to reconstruct two unknown interfering wavefronts using both numerical simulations and experiments.
- Analyzed a 3D interference pattern to effectively separate and identify the wavefronts involved.
- Utilized Zernike polynomials and a stochastic parallel gradient descent algorithm for wavefront expansion and calculations.
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- The paper focuses on designing and simulating conductive nanometric multilayer systems, specifically optimizing the thickness of Ag and ZnS layers for high transmittance and low sheet resistance.
- The ZnS/Ag/ZnS/Ag/ZnS (ZAZAZ) multilayer systems are created using a thermal evaporation method on glass substrates at room temperature.
- The ZAZAZ system achieves a sheet resistance of 2.7 Ω/sq and an optical transmittance of ~75.5%, and OLEDs built on this anode perform similarly to those using traditional indium-tin oxide anodes.
Nondiffracting Bessel-Gauss beams are assumed as the superposition of infinite numbers of Gaussian beams whose wave vectors lie on a cone. Based on such a description, different methods are suggested to generate these fields. In this paper, we followed an active scheme to generate these beams.
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- Studied how to create passive Bessel-Gauss beams using an axicon with a specially designed Gaussian resonator and measured the output from a Nd:YAG laser.
- Measured key properties of the beams such as output energy (58 mJ) and Rayleigh range (229.3 mm) for a 1° axicon, comparing them to the Gaussian mode results.
- Explored the effects of changing axicon apex angles and beam spot sizes on the properties of the generated Bessel-Gauss beams through both theoretical analysis and experiments.
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- The study introduces a new technique to evaluate intraocular lenses (IOLs) without needing surgical implantation.
- Three types of IOLs were tested in a model eye setup using an ocular adaptive optics system to analyze their performance.
- The evaluation involved measuring and modeling the subject's corneal shape and optical aberrations to accurately assess the lenses' impact on visual acuity.
Article Synopsis
- The compound eye research focuses on miniaturizing imaging systems, introducing a dual compound eye with three micro lens arrays featuring aspheric surfaces.
- This system operates in two states: as a superposition system capturing the entire field of view and as an apposition system that images only sections for a larger overall field of view.
- Additionally, implementing a field stop reduces stray light and optimizes the modulation transfer function (MTF) of the ideal superposition compound eye.