Residual Stresses Determination near FSW Joints by Combining the Hole Drilling Method and Reflection Hologram Interferometry

The results of residual stress characterization near friction stir welded (FSW) butt joint of aluminum plates are reported. The experimental analysis employs two-side measurements of local deformation response on small hole drilling by reflection hologram interferometry. The approach developed is based on the unequivocally solution of the properly posed inverse problem thus deriving both membrane and bending residual stress components. Residual stress components of high level are derived inside the tool shoulder borders on both specimen faces.

Verification of the accommodative responses in viewing an on-axis analog reflection hologram

Vergence and accommodation responses of human vision are very important factors when a 3D image is observed, and a vergence-accommodation conflict (VAC) causes perceptual distortion, visual discomfort, and fatigue for an observer. Theoretically, a hologram is expected to provide a 3D image without such a conflict. In this article, natural focusing was verified by human accommodation response (A-R) measurement during on-axis analog reflection Denisyuk hologram observation. The A-R of a group of participants were measured for a real marker and its Denisyuk hologram at various visualization distances using an Nvision K5001 autorefractor. The experimental results statistically confirmed the equivalence of the responses to the Denisyuk hologram and its real counterpart, as well as the absence of a VAC.

Влияние поляризации считывающей волны и циркулярного дихроизма на дифракционную эффективность отражательной голограммы в кубическом оптически активном фоторефрактивном поглощающем пьезокристалле

In the approximation of slowly varying amplitudes, a system of coupled waves equations is obtained, which is applicable for describing the diffraction and coupling of elliptically polarized light waves on a volume phase-amplitude holographic grating formed in a cubic optically active photorefractive absorbing piezoelectric crystal. The dependence of the diffraction efficiency of the phase reflection hologram on the ellipticity of the readout wave and the thickness of the Bi12SiO20 crystal of the (001) and (111) cuts was studied. The regularities of the effect of circular dichroism on the diffraction efficiency of the phase reflection hologram are analyzed. It is shown that for crystal of (001)-cut the maximum diffraction efficiency of the reflection hologram depending on the crystal thickness can be achieved using a readout wave both with linear polarization and with elliptical polarization. For crystal of (111)-cut the highest diffraction efficiency is achieved using a linearly polarized readout wave. It has been established that the effect of circular dichroism on the intensity of the reconstructed wave depends on the cut of the crystal, the ellipticity of the readout wave and the thickness of the crystal.

Mid-Infrared Grayscale Metasurface Holograms

Optical metasurfaces composed of two-dimensional arrays of densely packed nanostructures can project arbitrary holographic images at mid-infrared frequency. Our approach employs silicon nanopillars to control light properties, including polarization-independent phase response working with high-transmission efficiency over the 2π-phase modulation range at wavelength 4.7 μm. We experimentally dispose nanopillars accordingly to phase-only profiles calculated using the conventional Gerchberg–Saxton algorithm and revealed the optical performances of our devices using a mid-infrared on-axis optical setup. The total efficiency of our reflection hologram reaches 81%. Our experimental results agree well with the image of the desired object, opening up new perspectives for mid-infrared imaging and displaying for military, life science and sensing application.