RESUMEN
In this work, we present a new approach to retrieve the optical phase map of an object which is projected by a single differentiated two-beam interference pattern. This approach is based on the differentiation of the intensity equation of the two-beam interference with respect to the carrier's phase angle. Therefore, two interference patterns which are shifted by a very small phase angle can be obtained. Then, these two patterns are projected on the object. By exploiting the definition of the mathematical differentiation, the optical phase object's variations are retrieved from the recorded intensity distributions of both projected patterns. According to this method, the extracted optical phase angles are raised as an inverse "sin" function. This means that the unwrapping process of this function limits the recovered phase angles between - π/2 and π/2. So, the unwrapping process of these unusual wrapped phase angles is explained. The proposed method is applied on (a) two objects which are simulated by combinations of multiple Gaussian functions and (b) a 3D real object. It is found that the inclination of the projected interference pattern on the object redistributes the intensity distribution due to the Lamber's "cos" aw of illumination. This effect is considered in the retrieving process of the object's phase map. The limitations of the presented method are discussed and the obtained results are found promising.
RESUMEN
We have investigated the morphologies of Langmuir layers of charged, polymeric hard-core/interlayer/soft-shell nanoparticles spread at the air-water interface. Depending on various mutual interactions, which are correlated to the areal densities of the deposited nanoparticles, we observed ordered patterns of nondense and closed-packed arrangements of core/interlayer/shell (CIS) nanoparticle ordering. At low areal densities, we found an almost regular distribution of the charged CIS nanoparticles on the water surface, which resulted from long-range repulsive electrostatic interactions between them. At higher areal densities, domains of more closely packed and ordered nanoparticles were formed, coexisting with regions of randomly and sparsely distributed nanoparticles. We relate these domains to the interplay of electrostatic repulsion and capillary attraction caused by the dipolar character of like-charged particles at the interface, allowing for a characteristic separation distance between nanoparticles of about 3-4 times the nanoparticle diameter. At relatively high areal densities, attractive van der Waals forces were finally capable of making nanoparticles to come in contact with each other, leading to densely packed patches of hexagonally ordered nanoparticles coexisting with regions of rather well-ordered nanoparticles separated by about 1 µm and regions of randomly and sparsely distributed nanoparticles. Intriguingly, upon re-expansion of the area available per nanoparticle, these densely packed patches disappeared, indicating that steric repulsion due to the presence of soft shells as well as long-range electrostatic repulsive forces were strong enough to assure reversibility of the morphological behavior.
RESUMEN
In this paper, we introduced a mathematical method for measuring the optical path length differences (OPDs), which is suitable for large OPD values where the fringes connections are difficult to detect. The proposed method is based on varying the width of the fringes, without changing the wavelength of the used coherent source. Also, in this work, we discussed the need for such method in off-axis phase-shifting digital holography. Low-resolution off-axis holograms failed to detect the correct interference order. In general, off-axis phase-shifting digital holography is limited by the resolution of the captured holograms. The results obtained using our proposed technique were compared to the results obtained using off-axis phase-shifting digital holograms and conventional two-beam interferometry. Holograms were given for illustration.
RESUMEN
In this paper, we present a nonray-tracing technique for evaluating the three dimensional distribution of the refractive index values inside polymeric fibres. This technique, named 'single-frame computed-tomography (SFCT)', is applied to digital holography. A comparative study between the calculated optical phase values using ordinary tomography and SFCT is carried out, and a negligible deviation is detected. The proposed technique is used to determine the three-dimensional refractive index profile of isotactic Polypropylene fibres, IPP. The variation of the optical properties is measured before, during and after the formation of the necking phenomenon. In addition, SFCT technique is applied to the online determination of the change of the optical properties of IPP fibres. Holograms are given for illustration.
RESUMEN
We present a significant contribution to the theory of determining the refractive index profile of a bent homogenous optical fiber. In this theory we consider two different processes controlling the index profile variations. The first is the linear index variation due to stress along the bent radius, and the second is the release of this stress on the fiber surface. This release process is considered to have radial dependence on the fiber radius. These considerations enable us to construct the index profile in two dimensions normal to the optical axis, considering the refraction of light rays traversing the fiber. This theory is applied to optical homogenous bent fiber with two bending radii when they are located orthogonal to the light path of the object arm in the holographic setup (like the Mach-Zehnder interferometer). Digital holographic phase shifting interferometry is employed in this study. The recorded phase shifted holograms have been combined, reconstructed, and processed to extract the phase map of the bent optical fiber. A comparison between the extracted optical phase differences and the calculated one indicates that the refractive index profile variation should include the above mentioned two processes, which are considered as a response for stress distribution across the fiber's cross section. The experimentally obtained refractive index profiles provide the stress induced birefringence profile. Thus we are able to present a realistic induced stress profile due to bending.
RESUMEN
A direct measurement of the birefringence of a planar waveguide obtained by Na(+) -K(+) ion exchange was performed with a double Lloyd interferometer. The results are compared with those obtained by a roundrobin test involving the same sample. Birefringence of as much as Deltan = (2.0 +/- 0.2) x 10(-3) was measured.
RESUMEN
We present a nondestructive experimental method to measure monotonically varying refractive-index profiles of planar waveguides. The technique is a modification of the Lloyd's mirage setup proposed by Allman et al. [Appl. Opt. 33, 1806 (1994)] in order to have a reference phase distribution for the interference pattern. The theoretical calculations have been implemented to account for multiple reflections inside the sample. An application of the method to ion-exchanged glass waveguides is reported.