A phase imaging system based on complex field sensor is analyzed, and experiments are performed to verify three methods of phase retrieval, namely, multi-wavelength digital holography, multi-aperture Zernike wavefront sensing and coherent diffractive imaging. The diffracted wavefront scattered from an object (a randomly rough surface or a surface with a known feature) is captured with a CCD in the far-field and the wavefront phase at the object surface is reconstructed using an optimized iterative algorithm. Based on the method chosen, one or two diffraction patterns were captured. The results demonstrate the potential of the proposed complex field imaging sensor for in-situ quality control of additively manufactured objects.
Correlation of two dimensional (2D) images using photorefractive materials are first reviewed. The performance of a joint transform correlator based on photorefractive beam coupling is analyzed by determining the dependence of typical figures of merit such as the discrimination ratio, peak-to-correlation plane energy ratio, peak-to-noise ratio, etc. on the photorefractive gain coefficient and beam power ratio using typical reference and signal images. Furthermore, correlation of three dimensional (3D) images is introduced as the correlation of their 2D digital holograms. Critical figures of merit used for assessment of 2D correlation of images are applied to the correlation of holograms.
In our previous work, digital holographic topography has been used to investigate the depth pattern of different surfaces. Two-wavelength digital holography has been used to resolve depth variations on surfaces, which are in the order of several microns to centimeters. These holograms are reconstructed numerically by Fresnel diffraction to retrieve phase and intensity information, which reveals the three-dimensional topographic surface details. To determine the similarity/difference between two 3D objects, we have recently proposed a novel technique involving 2D correlation of holograms, where holograms constructed from sets of point sources in 3D space were simulated to demonstrate the feasibility of this method. Crosscorrelation of holograms can also be used to authenticate the quality of holograms, and for 3D image encryption. In this work, correlation of holograms, both computer-generated, as well as optically recorded from diffuse objects, will be investigated. Computer generated holograms are also created to mimic surface roughness of real 3D objects. Correlation can be used to evaluate the quality of the surfaces, such as objects fabricated by 3D manufacturing techniques.
In this paper we consider numerical model of an adaptive coherent fiber array system that is utilized for remote transmission of laser power to an active photovoltaic cell (PVC)-based receiver array. The PVC array performs optical-to-electrical power conversion, and provides a feedback signal that is sent to the laser transmitter via optical and/or RF link. The feedback signal is utilized for real-time adaptive shaping of laser power density distribution at the PVC array for achieving the following objectives:
(a) Minimization of laser power losses caused by mismatch between size and shape of the transmitter beam footprint and the PVC array. For optimal performance, the projected laser beam footprint should be adaptively changed to fit the PVC area under continuously changing turbulence strength, distance to the target, system field of view, platform jitter, etc. and
(b) Reduction of laser beam power fluctuations inside the PVC caused by errors in target/load tracking, and laser beam aimpointing and aimpoint stabilization.
In the numerical simulations the optical power with adaptive beam shaping was performed over 3 km and 7 km distances in turbulent atmosphere. The results demonstrate ability of the adaptive fiber array systems with 21 sub-apertures considered, for efficient adaptive beam shaping resulting in significant power beaming efficiency improvement.
A novel scintillation resistant wavefront sensor based on a densely packed array of classical Zernike filters, referred to as the multi-aperture Zernike wavefront sensor (MAZ-WFS), is introduced and analyzed through numerical simulations. Wavefront phase reconstruction in the MAZ-WFS is performed using iterative algorithms that are optimized for phase aberration sensing in severe atmospheric turbulence conditions. The results demonstrate the potential of the MAZ-WFS for high-resolution retrieval of turbulence-induced phase aberrations in strong scintillation conditions for atmospheric sensing and adaptive optics applications.
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