We present an experimental demonstration of a class of beams, namely Frozen Waves, that can carry predetermined longitudinal intensity profiles in the presence of modeled loss. These waveforms consist of a superposition of equal frequency Bessel beams with different transverse and longitudinal wavenumbers, and are generated using a programmable spatial light modulator addressed by computer-generated hologram. Attenuation-resistant Frozen Waves can address challenges associated with light-matter interaction in absorbing media encountered in imaging, remote sensing, and particle micro-manipulation, to name a few.
A method for improving the accuracy of surface shape measurement by multiwavelength holography is presented. In our holographic setup, a Bi12TiO20 photorefractive crystal was the holographic recording medium, and a multimode diode laser emitting in the red region was the light source in a two-wave mixing scheme. On employing such lasers the resulting holographic image appears covered with interference fringes corresponding to the object relief, and the interferogram spatial frequency is proportional to the diode laser's free spectral range (FSR). Our method consists in increasing the effective free spectral range of the laser by positioning a Fabry-Perot étalon at the laser output for mode selection. As larger effective values of the laser FSR were achieved, higher-spatial-frequency interferograms were obtained and therefore more sensitive and accurate measurements were performed. The quantitative evaluation of the interferograms was made through the phase-stepping technique, and the phase map unwrapping was carried out through the cellular-automata method. For a given surface, shape measurements with different interferogram spatial frequencies were performed and compared with respect to measurement noise and visual inspection.
The application of multi-wavelength holography for surface shape measurement is presented. In our holographic setup a Bi12TiO20 (BTO) photorefractive crystal was the holographic recording medium and a multimode diode laser emitting in the red region was the light source in a two-wave mixing scheme. The holographic imaging with multimode lasers results in multiple holograms in the BTO. By employing such lasers the resulting holographic image appears covered of interference fringes corresponding to the object relief and the interferogram spatial frequency is proportional to the diode laser free spectral range (FSR). We used a Fabry-Perot etalon at the laser output for laser mode selection. Thus, larger effective values of the laser FSR were achieved, leading to higher-spatial frequency interferograms and therefore to more sensitive and accurate measurements. The quantitative evaluation of the interferograms was performed through the phase stepping technique (PST) and the phase map unwrapping was carried out through the Cellular-Automata method. For a given surface, shape measurements with different interferogram spatial frequencies were performed and compared, concerning measurement noise and visual inspection.
This work reports a study of load transmission, evaluation and tension dissipation on dried human skull under loading simulation of isolated contraction (SIC) of some masticatories muscles by the phase-shifting real-time holography using photorefractive Bi12SiO20 crystal. The four-frames phase-shifting technique and the unwrapping branch-cut technique were used to obtain the phase map and quantitative results.
A novel method for surface profilometry by holography is presented. We used a diode laser emitting at many wavelengths simultaneously as the light source and a Bi12TiO20 (BTO) crystal as the holographic medium in single exposure processes. The employ of multi-wavelength, large free spectral range (FSR) lasers leads to holographic images covered of interference fringes corresponding to the contour lines of the studied surface. In order to obtain the relief of the studied surface, the fringe analysis was performed by the phase stepping technique (PST) and the phase unwrapping was carried out by the Cellular-automata method. We analysed the relief of a tilted flat metallic bar and a tooth prosthesis.
The phase-shifting interferometry techniques is a well-known technique which has been used with great success in optical profilers, micro-displacements, micro-deformations and others applications in Non-Destructive Test in basic research, engineering and biotechnology areas. This work presents our Advances in Phase-Shifting Real-Time Holography using Photorefractive Sillenite. And we have obtained quantitative results in many applications in measurements of micro-rotation, micro-displacements, deformation, surface contouring and whole lens wave-optics. The real-time holography process is doing using the photorefractive Bi12SiO20 crystal recording medium, where the phase-shifting 4-frames method for obtained the phase map, this was filtered by sin/cos filter and was applied the unwrapping process. The experimental results agree with the expected one in these applications and with promises potentialities of this method for studies with in situ visualization, monitoring and analysis.
Using digital holography the two-source method was applied for shape determination of a groove on an Aluminum plate. The electric component of the electromagnetic field, on the image plane, was reconstructed using the Fresnel-Kirchoff integral and Fourier method and digital holograms were captured changing the fiber optic position with a micro positioner. The phase interferogram was filtered by means of the sine/cosine filter and for the unwrapping process was applied the branch-cut method. This object present real discontinuity and the experimental results agree with the expected one, with high quality intensity image. The quasi-3D phase presentation shows the object shape.
This work applies a holographic interferometer setup that it uses the photorefractive Bi12SiO20 crystals for Real-Time Holographic Interferometry (RTHI) in diffusive regimen with configuration exhibiting difraction anisotropy. This device is connected with an interferogram-analysis method that uses the phase-stepping technique for quantitative measurement of changes on object. So we captured holographic interferograms from test surface, and calculated the phase map, using images by Four-Frame Method, and removed the wrapping of tangent function (unwrapping), using the Cellular-Automata Technique. We are obtained good results in applications in basic research, dentistry and technological areas.
In this work, we study self-focusing and self-defocusing effects, determination of photorefractive and thermal parameters in LiNbO3 and LiNbO3:Fe crystals using light-induced photorefractive and thermal lens with double-beam of mode-mismatched technique. Beyond to establish a best understand of photorefractive and thermal effects, their relations and limits in theses materials. And obtained good results in thermal lens effect (self-focusing) in LiNbO3 crystals and the photorefractive lens effect (self-focusing and self-defocusing).
The purpose of this work is the Study of Photorefractives Materials and their Applications in Optical and Holographic Information Processing. The process that makes possible these applications is the photorefractive effect. Thus, we study the propagation and coupling of electromagnetic waves in photorefractives materials: Bi12SiO20 (BSO) and Bi12TiO20 (BTO), and LiNbO3-doped and -undoped; both in bulk and fibers form. We use techniques of holographic characterization and nonlinear optics, for determination of parameters and figures of merit of these photorefractive medium. Also, present some applications, as: the use as holographic memories of high capacity of storage; and Non-Destructive Tests, as Real-Time Holographic Interferometry.
The Holographic interferometry is a non-destructive testing of analysis on surfaces in basic research, technological and biomedical fields. However, the holographic interferometry techniques in real-time with conventional materials present serious difficulties. The photorefractives crystal are present as an attractive holographic recording medium. The phenomenon that characterizes these crystals in the photorefractive effect, consists of the refractive index modulation through photo-induced and linear electro-optic effect, allows the register of holograms of phase. Also it presents advantages as in situ self-proceeding of the recording medium and its indefinite reusability, i.e. it does not present fatigue. Thus, the objective of this work is the development of a holographic interferometer that uses the photorefractive crystal of the selenite family Bi12SiO20 as holographic recording medium. In this direction, we search to characterize BSO crystal determining some figures of merit in diffusive regime and drift regime. The holographic techniques of metrology are presented in three methods: real time holographic interferometry, double- exposure holographic interferometry, and time-average holographic interferometry had been studied with some applications in analysis of statics and dynamics processes on surfaces.
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