Correcció de les aberracions d'un dispositiu de pinces òptiques hologràfiques mitjançant un sensor Shack-Hartmann

En aquest treball es presenten els principis físics de la captura de partícules micromètriques mitjançant les pinces òptiques hologràfiques, així com el sistema experimental que ho fa possible. La representació d'hologrames en un modulador espacial de llum permet generar patrons de trampes de manera dinàmica. Malauradament, aquest dispositiu introdueix aberracions òptiques que deterioren la qualitat de la trampa i poden impossibilitar la captura estable de partícules. S'han mesurat aquestes aberracions amb un sensor d'ones Shack-Hartmann, i s'ha calculat l'holograma que, escrit en el mateix modulador, permeti compensar-les. Això ha permès capturar i desplaçar partícules micromètriques de manera efectiva

Correcció de les aberracions d'un dispositiu de pinces òptiques hologràfiques mitjançant un sensor Shack-Hartmann

En aquest treball es presenten els principis físics de la captura de partícules micromètriques mitjançant les pinces òptiques hologràfiques, així com el sistema experimental que ho fa possible. La representació d'hologrames en un modulador espacial de llum permet generar patrons de trampes de manera dinàmica. Malauradament, aquest dispositiu introdueix aberracions òptiques que deterioren la qualitat de la trampa i poden impossibilitar la captura estable de partícules. S'han mesurat aquestes aberracions amb un sensor d'ones Shack-Hartmann, i s'ha calculat l'holograma que, escrit en el mateix modulador, permeti compensar-les. Això ha permès capturar i desplaçar partícules micromètriques de manera efectiva

Sistema de adquisición de datos autónomo para mediciones de campo de bandas de sombra durante eclipses solares

Projecte Final de Carrera d'Enginyeria Electrònica, Universitat de Barcelona, Facultat de Física. Director: José Bosch Estrada. Any: 2003.En el presente proyecto se ha desarrollado un sistema adquisición de datos autónomo para mediciones de campo de bandas de sombra, que es un fenómeno que se produce durante los minutos previos o posteriores a un eclipse total de Sol. El sistema consta de dos partes diferenciadas: un sistema de captación de las bandas con elementos fotosensibles, que incorpora etapas de amplificación y filtrado de las señales; un sistema independiente del anterior para digitalizar las señales captadas a una cierta frecuencia y grabarlas en una memoria Flash EEPROM, para poder descargar posteriormente los datos en un ordenador

HoloTrap: Interactive hologram design for multiple dynamic optical trapping

This work presents an application that generates real-time holograms to be displayed on a holographic optical tweezers setup; a technique that allows the manipulation of particles in the range from micrometres to nanometres. The software is written in Java, and uses random binary masks to generate the holograms. It allows customization of several parameters that are dependent on the experimental setup, such as the specific characteristics of the device displaying the hologram, or the presence of aberrations. We evaluate the software's performance and conclude that real-time interaction is achieved. We give our experimental results from manipulating 5 micron-diametre microspheres using the program.Comment: 17 pages, 6 figure

Design and characterization of thermally actuated bimetallic membranes by Michelson interferometry

This paper presents the design and characterization of thermally actuated Al-Si bimetallic membranes. The design was made with the Finite Element Method and was emphasized on optimizing the thickness ratio between the aluminum and silicon layers. The membrane deflection was measured employing the Michelson Interferometer. The experimental process was carried out with square membranes of 5 mm of side length, 10 mm in silicon thickness, and an aluminum thicknesses of 4 and 1 mm. A maximum deflection of 14 mm was obtained for membranes with 4 mm of aluminum thickness, which is consistent with predictions made by numerical calculations

Design strategies for optimizing holographic optical tweezers setups

We provide a detailed account of the construction of a system of holographic optical tweezers. While much information is available on the design, alignment and calibration of other optical trapping configurations, those based on holography are relatively poorly described. Inclusion of a spatial light modulator in the setup gives rise to particular design trade-offs and constraints, and the system benefits from specific optimization strategies, which we discuss.Comment: 16 pages, 15 figure

Correcció de les aberracions d'un dispositiu de pinces òptiques hologràfiques mitjançant un sensor de Shack-Hartmann

En aquest treball es presenten els principis físics de la captura de partícules micromètriques mitjançant les pinces òptiques hologràfiques, així com el sistema experimental que ho fa possible. La representació d'hologrames en un modulador espacial de llum permet generar patrons de trampes de manera dinàmica. Malauradament, aquest dispositiu introdueix aberracions òptiques que deterioren la qualitat de la trampa i poden impossibilitar la captura estable de partícules. S'han mesurat aquestes aberracions amb un sensor d'ones Shack-Hartmann, i s'ha calculat l'holograma que, escrit en el mateix modulador, permeti compensar-les. Això ha permès capturar i desplaçar partícules micromètriques de manera efectiva

Extending calibration-free force measurements to optically-trapped rod-shaped samples

Optical trapping has become an optimal choice for biological research at the microscale due to its non-invasive performance and accessibility for quantitative studies, especially on the forces involved in biological processes. However, reliable force measurements depend on the calibration of the optical traps, which is different for each experiment and hence requires high control of the local variables, especially of the trapped object geometry. Many biological samples have an elongated, rod-like shape, such as chromosomes, intracellular organelles (e.g., peroxisomes), membrane tubules, certain microalgae, and a wide variety of bacteria and parasites. This type of samples often requires several optical traps to stabilize and orient them in the correct spatial direction, making it more difficult to determine the total force applied. Here, we manipulate glass microcylinders with holographic optical tweezers and show the accurate measurement of drag forces by calibration-free direct detection of beam momentum. The agreement between our results and slender-body hydrodynamic theoretical calculations indicates potential for this force-sensing method in studying protracted, rod-shaped specimens

Artifact-free holographic light shaping through moving acousto-optic holograms

Holographic light modulation is the most efcient method to shape laser light into well-defned patterns and is therefore the means of choice for many intensity demanding applications. During the last two decades, spatial light modulators based on liquid crystals prevailed among several technologies and became the standard tool to shape light holographically. But in the near future, this status might be challenged by acousto-optic defectors. These devices are well known for their excelling modulation rates and high optical power resilience. But only few scattered precedents exist that demonstrate their holographic capabilities, despite the many interesting properties that they provide. We implemented a holographic acousto-optic light modulation (HALM) system, that is based on displaying holograms on acousto-optic defectors. We found that this system can eliminate the ubiquitous coherent artifacts that arise in holography through the inherent motion of acoustooptic holograms. That distinguishes our approach from any other holographic modulation technique and allows to reconstruct intensity patterns of the highest fdelity. A mathematical description of this efect is presented and experimentally confrmed by reconstructing images holographically with unprecedented quality. Our results suggest that HALM promotes acousto-optic defectors from highly specialized devices to full-fedged spatial light modulators, that can compete in a multitude of applications with LC-SLMs. Especially applications that require large optical output powers, high modulation speeds or accurate gray-scale intensity patterns will proft from this technology. We foresee that HALM may play a major role in future laser projectors and displays, structured illumination microscopy, laser material processing and optical trapping

Nonlinear filtering in object and Fourier space in a joint transform optical correlator: comparison and experimental realization

The use of different kinds of nonlinear filtering in a joint transform correlator are studied and compared. The study is divided into two parts, one corresponding to object space and the second to the Fourier domain of the joint power spectrum. In the first part, phase and inverse filters are computed; their inverse Fourier transforms are also computed, thereby becoming the reference in the object space. In the Fourier space, the binarization of the power spectrum is realized and compared with a new procedure for removing the spatial envelope. All cases are simulated and experimentally implemented by a compact joint transform correlator