Principios ópticos básicos aplicados al cálculo de los límites de métodos de difracción numérica

(Eng) The range of application of the methods of angular spectrum and Fresnel-Fraunhofer transform to compute numerical diffraction is evaluated via the basic optics concepts of Babinet´s principle and Frenel´s zones number. Conventionally, such limit is determined by assessing the correct sampling of the impulse response of the free space for each method as it evolves from the aperture to infinity. In this paper we make combined use of Babinet´s principle and Fresnel´s zones number to determine the phase that an optical wave field must exhibit after being propagated a given distance; the deviation of the phase of the optical field from the forecasted value is the metric utilized for testing the validity of the propagation method. The results show that the limit of application of the methods angular spectrum and Fresnel-Fraunhofer transform must be revisited. We propose a new limit that accounts for the number of pixels utilized for the correct sampling of a phase jump.(Spa) Para determinar el rango de aplicación de los métodos de difracción numérica espectro angular y transformada Fresnel-Fraunhofer, se han utilizado las nociones ópticas básicas del principio de Babinet y el concepto del número de zonas de Fresnel. Usualmente dicho límite se evalúa considerando el correcto muestreo de la respuesta al impulso en el espacio libre para cada método en su evolución desde la abertura hasta el infinito. En este trabajo se hace uso combinado del principio de Babinet y el número de zonas de Fresnel para determinar la fase que debe exhibir un campo óptico propagado numéricamente una distancia dada; la desviación de la fase del campo óptico del valor pronosticado constituye la métrica de evaluación de la validez del método de propagación. Los resultados obtenidos permiten concluir que el límite usado con frecuencia para dividir el rango de aplicación para los métodos de espectro angular y la transformada de Fresnel-Fraunhofer debe de ser revisado

Distinguishing fine details by Fresnel domain diffraction

ABSTRACT: The capability of distinguishing fine details in simple structures by means of Fresnel domain diffraction is shown. Through numerical simulations it is s hown that t he b igger Fresnel's number in the diffraction c onsidered the bigger differentiability is reached. A circular clear aperture with two fine details is employed for illustrating

Accurate single-shot quantitative phase imaging of biological specimens with telecentric digital holographic microscopy

The advantages of using a telecentric imaging system in digital holographic microscopy (DHM) to study biological specimens are highlighted. To this end, the performances of nontelecentric DHM and telecentric DHM are evaluated from the quantitative phase imaging (QPI) point of view. The evaluated stability of the microscope allows single-shot QPI in DHM by using telecentric imaging systems. Quantitative phase maps of a section of the head of the drosophila melanogaster fly and of red blood cells are obtained via single-shot DHM with no numerical postprocessing. With these maps we show that the use of telecentric DHM provides larger field of view for a given magnification and permits more accurate QPI measurements with less number of computational operations

Aberration compensation for objective phase curvature in phase holographic microscopy: comment

In a recent Letter by Seo et al. [Opt. Lett. 37, 4976 (2012)], the numerical correction of the quadratic phase distortion introduced by the microscope objective in digital holographic microscopy (DHM) has been presented. In this comment, we would like to draw to the attention of the authors and the readers in general that this approach could not be the optimal solution for maintaining the accuracy of the quantitative phase via DHM. We recall that the use of telecentric imaging systems in DHM simplifies the numerical processing of the phase images and produces more accurate measurements

Depth-resolved holographic reconstructions by three-dimensional deconvolution

Methods of three-dimensional deconvolution with a point-spread function as frequently employed in optical microscopy to reconstruct true three-dimensional distribution of objects are extended to holographic reconstructions. Two such schemes have been developed and are discussed: an instant deconvolution using the Wiener filter as well as an iterative deconvolution routine. The instant 3d-deconvolution can be applied to restore the positions of volume-spread objects such as small particles. The iterative deconvolution can be applied to restore the distribution of complex and extended objects. Simulated and experimental examples are presented and demonstrate artifact and noise free three-dimensional reconstructions from a single two-dimensional holographic record. Keywords: digital holography, volumetric deconvolution, three-dimensional volumetric deconvolution, particle tracking, holographic particle tracking, resolution, PSFComment: including MATLAB cod

XUV digital in-line holography using high-order harmonics

A step towards a successful implementation of timeresolved digital in-line holography with extreme ultraviolet radiation is presented. Ultrashort XUV pulses are produced as high-order harmonics of a femtosecond laser and a Schwarzschild objective is used to focus harmonic radiation at 38 nm and to produce a strongly divergent reference beam for holographic recording. Experimental holograms of thin wires are recorded and the objects reconstructed. Descriptions of the simulation and reconstruction theory and algorithms are also given. Spatial resolution of few hundreds of nm is potentially achievable, and micrometer resolution range is demonstrated.Comment: 8 pages, 8 figure

Field-portable reflection and transmission microscopy based on lensless holography

We demonstrate a lensfree dual-mode holographic microscope that can image specimens in both transmission and reflection geometries using in-line transmission and off-axis reflection holography, respectively. This field-portable dual-mode holographic microscope has a weight of ~200 g with dimensions of 15 x 5.5 x 5cm, where a laser source is powered by two batteries. Based on digital in-line holography, our transmission microscope achieves a sub-pixel lateral resolution of ≤2 µm over a wide field-of-view (FOV) of ~24 mm2 due to its unit fringe magnification geometry. Despite its simplicity and ease of operation, in-line transmission geometry is not suitable to image dense or connected objects such as tissue slides since the reference beam gets distorted causing severe aberrations in reconstruction of such objects. To mitigate this challenge, on the same cost-effective and field-portable assembly we built a lensless reflection mode microscope based on digital off-axis holography where a beam-splitter is used to interfere a tilted reference wave with the reflected light from the object surface, creating an off-axis hologram of the specimens on a CMOS sensor-chip. As a result of the reduced space-bandwidth product of the off-axis geometry compared to its in-line counterpart, the imaging FOV of our reflection mode is reduced to ~9 mm2, while still achieving a similar sub-pixel resolution of ≤2 µm. We tested the performance of this compact dual-mode microscopy unit by imaging a US-air force resolution test target, various micro-particles as well as a histopathology slide corresponding to skin tissue. Due to its compact, cost-effective, and lightweight design, this dual-mode lensless holographic microscope might especially be useful for field-use or for conducting microscopic analysis in resource-poor settings

Contrast-tuneable microscopy for single-shot real-time imaging

A novel real image in-line laser holography enables a tuneable image contrast, edge sharpness, and visualization of sub-wavelength structures, using a simple pair of filters and large-diameter lenses that can incorporate higher-order scattered light. Demonstrated also are the accuracy in object sizing and the ease of imaging along the focal depth, based on a single-shot imaging via holographic principle. In addition, the use of broad, collimated laser beam for irradiation has led to a wider field of view, making it particularly useful for an extensive monitoring of, and sweeping search for, cells and microbial colonies and for the real-time imaging of cancer-cell dynamics