Juan Soto, Fabio Aguilar Mora, José Rodrigo, Yana Geng, Nshunge Musheshe, Manon Buist-Homan, Frank Lezoualc'h, Xiaodong Cheng, Martina Schmidt, Han Moshage, Tatiana Alieva
Refractive index tomography compatible with conventional microscope is used for analyzing primary rat hepatocytes injury induced by pharmacological treatments. We found that mitochondria malfunctioning is correlated with refractive index variation.
Partially coherent optical diffraction tomography (PC-ODT) is a labelfree quantitative 3D imaging technique based on the refractive index contrast. It provides fast non-interferometric speckle noise-free imaging compatible with conventional wide-field transmission microscopes, but suffers from two principal inconveniences. One of them is the missing cone problem, which is a common drawback for all tomographic modalities with limited-angle inspection, including interferometric coherent ODT. The second one, considered in this paper, is a nonhomogeneous contrast for different spatial frequency regions. Analyzing the microscope 3D optical transfer functions for various illuminations over the condenser aperture we have found that the Gaussian illumination shape is a proper one. Numerical simulations and experimental results support this finding. A future line in the development of post-deconvolution processing is also discussed.
Different applications such as astronomy, remote optical sensing and free space optical communications, among others, require both numerical and laboratory experimental simulations of beam propagation through turbulent atmosphere prior to an outdoor test. While rotating phase plates or hot chambers can be applied to such studies, they do not allow changing the atmospheric conditions and the propagation distance in situ. In contrast, the spatial light modulators (SLMs) are a flexible alternative for experimental turbulence simulation. In this work we consider an experimental setup comprising two SLMs for studying laser beam propagation in weak atmospheric turbulence. The changes of atmospheric conditions and propagation distances are properly achieved by the adjustment of the phase screens and the focal distances of digital lenses implemented in both SLMs. The proposed system can be completely automatized and all its elements are in fixed positions avoiding mechanical misalignment. Its design, propagation distance and atmospheric condition adjustment are provided. The setup performance is verified by numerical simulation of Gaussian beam propagation in the weak turbulence regime. The obtained parameters: scintillation index, beam wander and spreading are compared to their theoretical counterparts for different propagation distances and atmospheric conditions.
Partially coherent light provides attractive benefits for different applications in microscopy, astronomy, telecommunications,
optical lithography, etc. However, design and generation of partially coherent beams with desirable
properties is challenging. Moreover, the experimental characterization of the spatial coherence is a difficult
problem involving second-order statistics represented by four-dimensional functions that cannot be directly measured
and analyzed. We discuss the techniques for design and generation of partially coherent structurally stable
beams and the recently developed phase-space tomography methods supported by simple experimental setups for
practical quantitative characterization of partially coherent light spatial structure, including its local coherence
properties.
We present a novel technique for coherence engineering of the microscope illumination based on a DLP projector providing fast (millisecond range) switchable both temporal and spatial coherence design. Its performance is experimentally demonstrated for speckle-noise free quantitative phase imaging with different spatial coherence states. Strategies for design and control of the light coherence are discussed.
We present a non-iterative holographic technique for efficient and versatile laser beam shaping along arbitrary 3D curves. Light beams with intensity shaped for several 3D curves: Tilted ring, Viviani’s curve, Archimedean spiral, and trefoil-knotted curve have been experimentally generated and applied for optical trapping of micrometer-sized dielectric particles. The high intensity gradients and independent phase control prescribed along the curve make this kind of laser trap attractive for multiple particle manipulation and allow for forward and backward motion to the light source. Indeed, different configurations of tractor beam traps are experimentally demonstrated. This technique can also be applied for laser micro-machining.
KEYWORDS: Tomography, Optical tomography, Commercial off the shelf technology, Spatial light modulators, Reconstruction algorithms, Current controlled current source, Charge-coupled devices, Digital video discs, Free space optics, Optical imaging
The application of partially coherent optical beams for imaging, free space communication, random medium analysis requires controlling its mutual intensity. This task can be done using the phase-space tomography method consisting on the reconstruction of the Wigner distribution (WD), and therefore the mutual intensity, from its projections associated with the fractional power spectra. We propose two schemes that apply spatial light modulators (SLMs) for the measurements of the required WD projections in the case of one- and two-dimensional optical signals. The use of the SLMs allows rapid data acquisition and operative change of the projection number. Moreover, the measured intensity distributions do not require further rescaling, which accelerates the WD reconstruction algorithm and improves its efficiency. The developed numerical methods provide different ways for data analysis such as the reconstruction of the WD using the inverse Radon transform and its visualization for the case of one-dimensional signals; the determination of the mutual intensity for two fixed points without previous reconstruction of the entire WD for two-dimensional signals, etc. The validity of the proposed approaches has been verified experimentally for the test signals and the results are in a good agreement with the numerical simulations.
The fractional Fourier transform (FT) is a powerful tool with relevant applications in optical and digital information
processing. Such applications demand a programmable and versatile optical system able to perform the
fractional FT almost at real time. We have recently developed an optical setup satisfying these requirements.
In contrast with other proposed setups, it offers the following advantages: the operation is achieved without
additional scaling and/or phase factors and a minimal number of lenses, located at fixed position, are utilized.1
In this work we present the main design features of the fractional FT processor and discuss its performance for
some relevant applications.
We present an overview of the main properties and the emerging implementations corresponding to a photopolymerizable glass modified with high refractive index species (HRIS) incorporated at molecular level. The study concerns to transmission and reflection holograms in Bragg and Raman-Nath regimens and polarization properties of
gratings with high spatial frequencies are also analyzed demonstrating a strong dependence of the refractive index
modulation with the polarization state of the reading beam. Not limited to the study of the optical properties of the
photopolymerizable glass we propose two applications of the holographic material. The first one is the fabrication of
polarizers elements with high performance at low cost such us holographic polarizers and holographic polarizers beam splitters. The second application concerns to the holographic recording of stables modes exhibiting high diffraction efficiency. Also, we have recently extended our studies to ultrashort pulse lasers in femtosecond regime. The photopolymerizable gratings are good candidates as optic elements to beam manipulation of ultrashort pulse lasers.
We report recent results obtained with volume holographic gratings recorded in a new photopolymerisable glass
modified with high refractive index species at molecular level. Various not previously observed performances have been
achieved for diffraction efficiency and angular selectivity. In particular, new overmodulation effects have been observed
for the first time experimentally in an amorphous material.
KEYWORDS: Holography, Holograms, Digital holography, Diffraction, Digital video discs, Video, Digital recording, Spatial light modulators, Physics, Multimedia
In this work we present a Virtual Holographic Laboratory for educational purposes. This project is edited on DVD support and it has been designed to be interactive: schemes, pictures, videos in order to clarify the theoretical description of the phenomena improving the understanding of its fundamental concepts. We believe that this project is helpful for undergraduate and graduate students in physics and engineering to obtain the solid knowledge about holography and to prepare for practical lessons on holography or partially substitute the lasts in the case of absence of appropriated technical base at a specific university level.
Wide application of the laser beams in science, technology and biomedicine demands the generation of the beams with desirable structure. In particular for optical trapping the beams with high transversal gradient of intensity distribution or doughnut like structures which carried out the orbital angular momentum are designed. In the recent study of the diffraction on the fractal Cantor zone plates [1-5] the possibility to generate the beams with capsule like structure (closed cylinder with the axis along the direction of beam propagation) for a certain distances has been discovered [5]. This peculiar form of the beam can be used for three dimensional particle trapping. Nevertheless the fractal zone plates are not unique gratings that generate this type of structures.
We study experimentally and by numerical simulation the Fresnel diffraction on the recently introduced fractal zone plates (ZPs) associated with Cantor sets. The focusing properties of these ZPs and the evolution of the intensity patterns at the plane transversal to the propagation direction are discussed. As it follows from numerical simulation the series of conventional and doughnut-like secondary focuses are observed around the principal focus. The position, depth and the size of these focuses depends on the type of Cantor set and the level of the fractal, which are directly related to the number of the corresponding Fresnel zones. The results obtained by numerical simulations are verified in the experiments. The fractal Cantor ZPs of different levels are implemented with a liquid crystal display and with the diapositives. The experimental results obtained by both types of the dispositives are in good agreement with the theory and numerical simulations.
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