Marcos R. R. Gesualdi

Frozen waves: experimental generation

Frozen waves (FWs) are very interesting particular cases of nondiffracting beams whose envelopes are static and whose longitudinal intensity patterns can be chosen a priori. We present here for the first time (that we know of) the experimental generation of FWs. The experimental realization of these FWs was obtained using a holographic setup for the optical reconstruction of computer generated holograms (CGH), based on a 4-f Fourier filtering system and a nematic liquid crystal spatial light modulator (LC-SLM), where FW CGHs were first computationally implemented, and later electronically implemented, on the LC-SLM for optical reconstruction. The experimental results are in agreement with the corresponding theoretical analytical solutions and hold excellent prospects for implementation in scientific and technological applications.

Modeling the spatial shape of nondiffracting beams: Experimental generation of Frozen Waves via holographic method

In this paper we experimentally implement the spatial shape modeling of nondiffracting optical beams via computer generated holograms reconstructed optically by spatial light modulators. The results reported here are an experimental confirmation of the so-called Frozen Wave method, developed a few years ago. Optical beams of this type have potential applications in optical tweezers, medicine, atom guiding, remote sensing, etc.

Measurement of the thermo-optic coefficient in liquids by laser-induced conical diffraction and thermal lens techniques

We report on a method to determine the temperature coefficient of the refractive index (dn/dT) for non-fluorescent liquids which is based on the experimental observation of conical diffraction induced by self-phase modulation (SPM). Light absorbing impurities were added to allow for heat deposition by the excitation laser beam. We studied samples of tetrahydrofuran (THF, C4H8O) and toluene (C6H5CH3) with suspended cadmium selenide/zinc sulfide (CdSe/ZnS) core–shell quantum dots as absorbing impurities and samples of water (H2O) and THF with a small addition of blue-black commercial ink. The well-known thermal lens (TL) technique was also employed in this work for the sake of comparison with the proposed conical diffraction pattern. Thermo-optical parameters obtained by the mode-mismatched thermal lens (TL) technique validated the SPM measurements of dn/dT. In addition, we applied in this work the Fresnel–Kirchhoff diffraction formalism for the theoretical prediction of the rings that are observed in the far-field region. The technique proposed herein to determine dn/dT may serve as a fast, cost-effective optical method for evaluating adulterated or impure chemicals.

Mastication effort study using photorefractive holographic interferometry technique

The purpose of this work was the force-displacement response analysis of the masticatory process in a dried human skull by Double-Exposure Photorefractive Holographic Interferometry Technique (2E-PRHI). The load concentration and dissipation of the forces from dried human skull were analysed at applied loading stands as a Simulation of Isolated Contraction (SIC) of some mastication muscles. The 2EHI and Fringe Analysis Method were used to obtain the quantitative results of this force-displacement response. These results document quantitatively the real biomechanical response from dried human skull under applied loading and it can be used for complementary study by finite element model and others analysis type.

Phase-shifting real-time holographic interferometry applied to load transmission evaluation in dried human skull

Phase-shifting real-time holography with photorefractive Bi(12)SiO(20) crystal as holographic recording medium applied to load transmission evaluation and tension dissipation on a dried human skull under loading is presented. The applied loading stands as a simulation of isolated contraction (SIC) of some masticatories muscles. The four-frames phase-shifting technique and the unwrapping branch-cut technique were used to obtain the phase map. The quantitative results show the feasibility of the employed system in the study of microdisplacements in the skull structure provided by SIC.

Enhanced multiwavelength holographic profilometry by laser mode selection

A method for improving the accuracy of surface shape measurement by multiwavelength holography is presented. In our holographic setup, a Bi 12 TiO 20 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 lasers free spectral range (FSR). Our method consists in increasing the effective free spectral range of the laser by positioning a Fabry-Perot etalon 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.

Production of dynamic frozen waves: controlling shape, location (and speed) of diffraction-resistant beams

In recent times, we experimentally realized quite an efficient modeling of the shape of diffraction-resistant optical beams, thus generating for the first time the so-called frozen waves (FW), whose longitudinal intensity pattern can be arbitrarily chosen within a prefixed space interval of the propagation axis. In this Letter, we extend our theory of FWs, which led to beams endowed with a static envelope, through a dynamic modeling of the FWs whose shape is now allowed to evolve in time in a predetermined way. Further, we experimentally create such dynamic FWs (DFWs) in optics via a computational holographic technique and a spatial light modulator. Experimental results are presented here for two cases of DFWs, one of zeroth order and the other of higher order, the latter being the most interesting exhibiting a cylindrical surface of light whose geometry changes in space and time.

Photorefractive and computational holography in the experimental generation of Airy beams

Abstract In this paper, we present the experimental generation of Airy beams via computational and photorefractive holography. Experimental generation of Airy beams using conventional optical components presents several difficulties and a practically infeasible. Thus, the optical generation of Airy beams has been made from the optical reconstruction of a computer generated hologram implemented by a spatial light modulator. In the photorefractive holography technique, being used for the first time to our knowledge, the hologram of an Airy beam is constructed (recorded) and reconstructed (read) optically in a nonlinear photorefractive medium. The Airy beam experimental realization was made by a setup of computational and photorefractive holography using a photorefractive Bi 12 TiO 20 crystal as holographic recording medium. Airy beams and Airy beam arrays were obtained experimentally in accordance with the predicted theory; with excellent prospects for applications in optical trapping and optical communications systems.

Two-source method in digital holographic contouring

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.

Experimental demonstration of attenuation resistant frozen waves

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.