P. A. M. dos Santos

Topological defects in moiré fringes with spiral zone plates

We present a study of spatial structures created by superposition of spiral zone plates used for generating optical beams with phase singularities. Moiré fringes are observed that show topological defects similar to those appearing in interference patterns of optical vortices. A brief theoretical discussion is included that supports the similarities between the two phenomena. Our results may lead to interesting applications to digital information processing by optical means.

Optical activity measurements in the photorefractive Bi12TiO20 single crystal fibers

Abstract In the present work the specific optical activity coefficient of the photorefractive Bi 12 TiO 20 single crystal fibers have been determined. The samples were illuminated by λ =0.6328 μ m and λ =0.5145 μ m. The proposed experimental technique is simple, fast and accurate. It is based on the automatic electronic phase shift detection in a dynamic polarimetric system. 6.62±0.06 deg/mm was obtained for λ =0.633 μ m and 10.0±0.2 deg/mm for λ =0.514 μ m.

Moiré-like patterns as a spatial beat frequency in photorefractive sinusoidal phase gratings superposition

Abstract Dynamic Moire-like patterns generation by the superposition of two dynamic sinusoidal phase gratings is described. Two sinusoidal phase gratings of slightly different pitches are involved and occur in the photorefractive crystal Bi 12 TiO 20 (BTO). This holographic dynamic medium has been used in anisotropic two wave mixing architecture in diffusion only recording mechanism.

Polarization influence in the photorefractive and absorption grating decays in the Bi12TiO20

Abstract In the present paper, experimental evidence that the polarization of writing beams influences the interaction between photorefractive and absorption grating decays, producing or not a field enhancement in the light diffracted by the gratings, is demonstrated. The experimental results are related to sinusoidal phase grating decays and account of the anisotropic diffraction viewpoint. The measurements were performed in diffusion only recording mechanism in the photorefractive crystal Bi 12 TiO 20 illuminated by λ = 0.633 µm from a He-Ne laser light source.

Dynamic moiré patterns for profilometry applications

In the present work is proposed that dynamic moire-like fringe patterns produced by photorefraction, with low spatial frequencies, could be used for profile determination of small objects. The Fourier transform profilometry technique is applied in the projected moire fringe pattern onto an object surface. Basically, the Fourier transform of the projected fringes is obtained. After that, a phase map is generated. Then, the optical profile of object is obtained using phase unwrapping. So, the entire process can be indicated to measure, with good accuracy degree, profile of small objects in sub-micrometer scale in optical mechanical systems.

Photorefractive sensitivity characterization of a BSO-type crystal by anisotropic self-diffraction

Abstract In this note attention is given to the holographic characterization of photorefractive sensitivity by the spatial light modulation dependence in a Bi 12 TiO 20 crystal. A sample in the diffusion-only Bragg regime was used. The experiment improves the anisotropic self-diffraction properties of the material. Through this method, it is possible to find the best conditions for the fast response of the material when used as an optical holographic processor.

Shear strain determination of the polymer polydimethysiloxane (PMDS) using digital image correlation in different temperatures

In the present work a digital image correlation (DIC) method is used in order to analyze the adhesive shear modulus of poly-dimethylsiloxane (PDMS) submitted to different loads and temperatures. This is an optical-numerical full-field surface displacement measurement method. It is based on a comparison between two images of a specimen coated by a random speckled pattern in the undeformed and in the deformed states. A single lap joint testing is performed. This is a standard test specimen for characterizing adhesive properties and it is considered the simplest form of adhesive joints. For the single lap joint specimen, steel adherends are bonded using a flexible rubber elastic polymer (PDMS), which is a commercially available silicone elastic rubber

Automatic optical activity measurement system

The present note proposes a simple, fast and accurate experimental technique to measure the specific optical activity coefficients in fibre-like crystals. The system is based on the automatic electronic phase shift detection by a lock-in amplifier in a dynamic polarimetric system.

Holographic image degradation produced by mechanical stress in the photorefractive crystal

Abstract In this work we show the real time holographic image degradation produced by mechanical stress applied to a cubic photorefractive crystal of the sillenite family. The observations were performed in a diffusion only recording mechanisms in the photorefractive crystal Bi 12 TiO 20 illuminated by λ =0.633 μ m from a He–Ne laser light source. Our results can be easily extended to all BSO-type crystals where the continuous image reconstruction exploits the anisotropic diffraction.

Dynamic moiré patterns produced by sinusoidal gratings superposition in the Bi12 TiO20 crystal

Abstract In the present note a real-time holographic moire-like pattern is shown. It is produced by the superposition of two rotated sinusoidal phase gratings and the result represents a promising technique for possible metrological applications. The experiments were performed in a diffusion-only recording mechanism in a photorefractive Bi 12 TiO 20 crystal illuminated by λ = 0.633 μm from a HeNe laser light source.