Raúl Castañeda

Numerical wave propagation in ImageJ.

An ImageJ plugin for numerical wave propagation is presented. The plugin provides ImageJ, the well-known software for image processing, with the capability of computing numerical wave propagation by the use of angular spectrum, Fresnel, and Fresnel-Bluestein algorithms. The plugin enables numerical wave propagation within the robust environment provided by the complete set of built-in tools for image processing available in ImageJ. The plugin can be used for teaching and research purposes. We illustrate its use to numerically recreate Poissons spot and Babinets principle, and in the numerical reconstruction of digitally recorded holograms from millimeter-sized and pure phase microscopic objects.

Automatic full compensation of quantitative phase imaging in off-axis digital holographic microscopy

An automatic method that fully compensates the quantitative phase measurements in off-axis digital holographic microscopy (DHM) is presented. The two main perturbations of the quantitative phase measurements in off-axis DHM are automatically removed. While the curvature phase flaw introduced by the microscope objective is avoided by the use of an optimized telecentric imaging system for the recording of the holograms, the remaining phase perturbation due to the tilt of the reference wave is removed by the automatic computation of a digital compensating reference wave. The method has been tested on both nonbiological and biological samples with and improving on the quality of the recovered phase maps.

Single-shot 3D topography of reflective samples with digital holographic microscopy

In this work, an off-axis digital holographic microscope operating in reflection mode and a telecentric regimen to produce 3D topography of a microscopy sample is shown. The main characteristics of the proposed method, which make it different from the previous works in the field, are the possibility of producing the 3D topography by a single shot over the complete field of view with sensitivity of λ/100, without phase perturbations introduced by the illuminating-imaging system, and with no further numerical processing beyond that required for recovering the phase map of the sample. A complete analysis of the illuminating-imaging system of the digital holographic microscope is presented. The proposed digital holographic microscope is tested on imaging a USAF resolution test target and some micro-electromechanical systems (MEMs).

Experimental study of the effects of the spatial filtering on off-axis digital holography operating out and in of the diffraction limit

espanolEn este trabajo se hace un analisis teorico y experimental de la estrecha relacion que existe entre el registro de hologramas digitales operando o no en el limite de difraccion y del proceso de filtrado espacial en el desempeno global de la reconstruccion numerica de hologramas registrados digitalmente. Los resultados obtenidos permiten concluir que no es posible hacer un filtrado espacial correcto del holograma para su posterior reconstruccion numerica, si el registro de holograma no es realizado en el limite de difraccion o en su defecto sin solapamiento de los ordenes de difraccion. EnglishThis paper presents a theoretical and experimental analysis of the close relationship between the recording of digital holograms operating out or in of the diffraction limit and the spatial filtering process in the overall performance of the numerical reconstruction of the digitally recorded holograms. The results allow to conclude that it is not possible to make a correct spatial filtering for a reliable numerical reconstruction of the recorded holograms, if the recording is not made in the diffraction limit or presents overlapping of the diffraction orders.

Limits of numerical diffraction methods revisited

An optical field can be numerical propagated using the method of the angular spectrum and Fresnel transform. The limits of application for these two numerical methods to compute the propagation of optical fields are evaluated.