Publications by authors named "Ángel Lizana"

23 Publications

  • Page 1 of 1

Customized depolarization spatial patterns with dynamic retardance functions.

Sci Rep 2021 May 3;11(1):9415. Epub 2021 May 3.

Departamento de Física, Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain.

In this work we demonstrate customized depolarization spatial patterns by imaging a dynamical time-dependent pixelated retarder. A proof-of-concept of the proposed method is presented, where a liquid-crystal spatial light modulator is used as a spatial retarder that emulates a controlled spatially variant depolarizing sample by addressing a time-dependent phase pattern. We apply an imaging Mueller polarimetric system based on a polarization camera to verify the effective depolarization effect. Experimental validation is provided by temporal integration on the detection system. The effective depolarizance results are fully described within a simple graphical approach which agrees with standard Mueller matrix decomposition methods. The potential of the method is discussed by means of three practical cases, which include non-reported depolarization spatial patterns, including exotic structures as a spirally shaped depolarization pattern.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-021-88515-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8093234PMC
May 2021

Polarimetric imaging microscopy for advanced inspection of vegetal tissues.

Sci Rep 2021 Feb 16;11(1):3913. Epub 2021 Feb 16.

Grup D'Òptica, Physics Department, Universitat Autònoma de Barcelona, 08193, Bellaterra, Spain.

Optical microscopy techniques for plant inspection benefit from the fact that at least one of the multiple properties of light (intensity, phase, wavelength, polarization) may be modified by vegetal tissues. Paradoxically, polarimetric microscopy although being a mature technique in biophotonics, is not so commonly used in botany. Importantly, only specific polarimetric observables, as birefringence or dichroism, have some presence in botany studies, and other relevant metrics, as those based on depolarization, are underused. We present a versatile method, based on a representative selection of polarimetric observables, to obtain and to analyse images of plants which bring significant information about their structure and/or the spatial organization of their constituents (cells, organelles, among other structures). We provide a thorough analysis of polarimetric microscopy images of sections of plant leaves which are compared with those obtained by other commonly used microscopy techniques in plant biology. Our results show the interest of polarimetric microscopy for plant inspection, as it is non-destructive technique, highly competitive in economical and time consumption, and providing advantages compared to standard non-polarizing techniques.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-021-83421-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7887219PMC
February 2021

Depolarization metric spaces for biological tissues classification.

J Biophotonics 2020 08 25;13(8):e202000083. Epub 2020 May 25.

Grup d'Òptica, Physics Department, Universitat Autònoma de Barcelona, Bellaterra, Spain.

Classification of tissues is an important problem in biomedicine. An efficient tissue classification protocol allows, for instance, the guided-recognition of structures through treated images or discriminating between healthy and unhealthy regions (e.g., early detection of cancer). In this framework, we study the potential of some polarimetric metrics, the so-called depolarization spaces, for the classification of biological tissues. The analysis is performed using 120 biological ex vivo samples of three different tissues types. Based on these data collection, we provide for the first time a comparison between these depolarization spaces, as well as with most commonly used depolarization metrics, in terms of biological samples discrimination. The results illustrate the way to determine the set of depolarization metrics which optimizes tissue classification efficiencies. In that sense, the results show the interest of the method which is general, and which can be applied to study multiple types of biological samples, including of course human tissues. The latter can be useful for instance, to improve and to boost applications related to optical biopsy.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jbio.202000083DOI Listing
August 2020

Influence of temporal averaging in the performance of a rotating retarder imaging Stokes polarimeter.

Opt Express 2020 Apr;28(8):10981-11000

We study the optimum operating conditions for a rotating retarder fixed polarizer (RRFP) when the measurements are not quasi-instantaneous but time-averaged. We obtain the optimum retardance and retarder orientations as a function of the integrated angle interval. We also study how the increase in the number of time-averaged measurements leads to a better equally weighted variance (EWV) value, and thus, to a better performance of the polarimeter in terms of noise amplification for the case of additive noise. Two different analyzers configurations are studied in this work: uniformly spaced retarder angles and when measurements are taken at optimum angles (non-uniformly spaced angles). We also consider the case of polychromatic illumination. We discuss the best measurement conditions in terms of the signal-to-noise ratio depending on whether there is a fixed or a limited amount of photons per measurement.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OE.385623DOI Listing
April 2020

Depolarizing metrics for plant samples imaging.

PLoS One 2019 14;14(3):e0213909. Epub 2019 Mar 14.

Grup d'Òptica, Physics Department, Universitat Autònoma de Barcelona, Bellaterra, Spain.

Optical methods, as fluorescence microscopy or hyperspectral imaging, are commonly used for plants visualization and characterization. Another powerful collection of optical techniques is the so-called polarimetry, widely used to enhance image contrast in multiple applications. In the botanical applications framework, in spite of some works have already highlighted the depolarizing print that plant structures left on input polarized beams, the potential of polarimetric methods has not been properly exploited. In fact, among the few works dealing with polarization and plants, most of them study light scattered by plants using the Degree of Polarization (DoP) indicator. Other more powerful depolarization metrics are nowadays neglected. In this context, we highlight the potential of different depolarization metrics obtained using the Mueller matrix (MM) measurement: the Depolarization Index and the Indices of Polarimetric Purity. We perform a qualitative and quantitative comparison between DoP- and MM-based images by studying a particular plant, the Hedera maroccana. We show how Mueller-based metrics are generally more suitable in terms of contrast than DoP-based measurements. The potential of polarimetric measurements in the study of plants is highlighted in this work, suggesting they can be applied to the characterization of plants, plant taxonomy, water stress in plants, and other botanical studies.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0213909PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6417720PMC
December 2019

Generation of reconfigurable optical traps for microparticles spatial manipulation through dynamic split lens inspired light structures.

Sci Rep 2018 Jul 26;8(1):11263. Epub 2018 Jul 26.

Universitat Autónoma de Barcelona, Physics Department, Optics Group, Bellaterra, 08193, Spain.

We present an experimental method, based on the use of dynamic split-lens configurations, useful for the trapping and spatial control of microparticles through the photophoretic force. In particular, the concept of split-lens configurations is exploited to experimentally create customized and reconfigurable three-dimensional light structures, in which carbon coated glass microspheres, with sizes in a range of 63-75 μm, can be captured. The generation of light spatial structures is performed by properly addressing phase distributions corresponding to different split-lens configurations onto a spatial light modulator (SLM). The use of an SLM allows a dynamic variation of the light structures geometry just by modifying few control parameters of easy physical interpretation. We provide some examples in video format of particle trapping processes. What is more, we also perform further spatial manipulation, by controlling the spatial position of the particles in the axial direction, demonstrating the generation of reconfigurable three-dimensional photophoretic traps for microscopic manipulation of absorbing particles.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1038/s41598-018-29540-1DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6062552PMC
July 2018

Methods for the performance enhancement and the error characterization of large diameter ground-based diffractive telescopes.

Opt Express 2017 Oct;25(22):26662-26677

This paper is devoted to the improvement of ground-based telescopes based on diffractive primary lenses, which provide larger aperture and relaxed surface tolerance compared to non-diffractive telescopes. We performed two different studies devised to thoroughly characterize and improve the performance of ground-based diffractive telescopes. On the one hand, we experimentally validated the suitability of the stitching error theory, useful to characterize the error performance of subaperture diffractive telescopes. On the other hand, we proposed a novel ground-based telescope incorporated in a Cassegrain architecture, leading to a telescope with enhanced performance. To test the stitching error theory, a 300 mm diameter, 2000 mm focal length transmissive stitching diffractive telescope, based on a three-belt subaperture primary lens, was designed and implemented. The telescope achieves a 78 cy/mm resolution within 0.15 degree field of view while the working wavelength ranges from 582.8 nm to 682.8 nm without any stitching error. However, the long optical track (35.49 m) introduces air turbulence that reduces the final images contrast in the ground-based test. To enhance this result, a same diameter compacted Cassegrain ground-based diffractive (CGD) telescope with the total track distance of 1.267 m, was implemented within the same wavelength. The ground-based CGD telescope provides higher resolution and better contrast than the transmissive configuration. Star and resolution tests were experimentally performed to compare the CGD and the transmissive configurations, providing the suitability of the proposed ground-based CGD telescope.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OE.25.026662DOI Listing
October 2017

Error analysis of large-diameter subaperture stitching Fresnel diffractive elements.

Appl Opt 2017 Sep;56(27):7672-7678

Image quality is dramatically influenced by the stitching errors in a large-diameter stitching Fresnel lens. In this paper, we studied three kinds of errors that can cover all stitching errors in a Cornwell deployed Fresnel lens. In particular, a 300-mm-diameter, three-belt deployed Fresnel diffractive lens was simulated to investigate the stitching error. The star test and the resolution board test experiments were conducted, and the experimental results fit the simulation results. This means that our error analysis theory and simulation method are efficient and accurate and could be used to guide future super-large aperture stitching.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/AO.56.007672DOI Listing
September 2017

Dual polarization split lenses.

Opt Express 2017 Oct;25(20):23773-23783

We report the realization of polarization sensitive split lens configurations. While split lenses can be used to easily generate different types of controlled structured light patterns, their realization has been limited so far to scalar beams. Here we propose and experimentally demonstrate their generalization to vectorial split lenses, leading to light patterns with customized intensity and state of polarization. We demonstrate how these polarization split lenses can be experimentally implemented by means of an optical system using two liquid crystal spatial light modulators, each one phase modulating one orthogonal polarization component. As a result, we demonstrate the experimental generation of vectorial beams with different shapes generated with these dual polarization split lenses. Excellent experimental results are provided in each case. The proposed technique is a simple method to generate structured light beams with polarization diversity, with potential applications in polarimetry, customized illuminators or quantum optics.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OE.25.023773DOI Listing
October 2017

Synthesis and characterization of depolarizing samples based on the indices of polarimetric purity.

Opt Lett 2017 Oct;42(20):4155-4158

In this work, we discuss the interest of using the indices of polarimetric purity (IPPs) as a criterion for the characterization and classification of depolarizing samples. We prove how differences in the depolarizing capability of samples, not seen by the commonly used depolarization index P, are identified by the IPPs. The above-stated result is analyzed from a theoretical point of view and experimentally verified through a set of polarimetric measurements. We show how the approach presented here can be useful in easily synthetizing depolarizing samples with controlled depolarizing features, just by properly combining low-cost fully polarizing elements (such as linear retarders or polarizers).
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OL.42.004155DOI Listing
October 2017

Polarimetric imaging of biological tissues based on the indices of polarimetric purity.

J Biophotonics 2018 04 12;11(4):e201700189. Epub 2017 Dec 12.

Grup d'Òptica, Physics Department, Universitat Autònoma de Barcelona, Bellaterra, Spain.

We highlight the interest of using the indices of polarimetric purity (IPPs) to the inspection of biological tissues. The IPPs were recently proposed in the literature and they result in a further synthetization of the depolarizing properties of samples. Compared with standard polarimetric images of biological samples, IPP-based images lead to larger image contrast of some biological structures and to a further physical interpretation of the depolarizing mechanisms inherent to the samples. In addition, unlike other methods, their calculation do not require advanced algebraic operations (as is the case of polar decompositions), and they result in 3 indicators of easy implementation. We also propose a pseudo-colored encoding of the IPP information that leads to an improved visualization of samples. This last technique opens the possibility of tailored adjustment of tissues contrast by using customized pseudo-colored images. The potential of the IPP approach is experimentally highlighted along the manuscript by studying 3 different ex-vivo samples. A significant image contrast enhancement is obtained by using the IPP-based methods, compared to standard polarimetric images.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1002/jbio.201700189DOI Listing
April 2018

Polarization gating based on Mueller matrices.

J Biomed Opt 2017 05;22(5):56004

Universitat Autònoma de Barcelona, Grup d'Òptica, Physics Department, Bellaterra, Spain.

We present mathematical formulas generalizing polarization gating (PG) techniques. PG refers to a collection of imaging methods based on the combination of different controlled polarization channels. In particular, we show how using the measured Mueller matrix (MM) of a sample, a widespread number of PG configurations can be evaluated just from analytical expressions based on the MM coefficients. We also show the interest of controlling the helicity of the states of polarization used for PG-based metrology, as this parameter has an impact in the image contrast of samples. In addition, we highlight the interest of combining PG techniques with tools of data analysis related to the MM formalism, such as the well-known MM decompositions. The method discussed in this work is illustrated with the results of polarimetric measurements done on artificial phantoms and real ex-vivo tissues.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1117/1.JBO.22.5.056004DOI Listing
May 2017

Complete snapshot Stokes polarimeter based on a single biaxial crystal.

Opt Lett 2016 Oct;41(19):4566-4569

We propose a new complete snapshot Stokes polarimeter based on a single biaxial crystal. It presents different strengths (snapshot, complete polarimetric measurements, large data redundancy, and high sensitivity) in a simple and compact optical arrangement. The polarimeter is experimentally implemented and analyzed in terms of accuracy and repeatability.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OL.41.004566DOI Listing
October 2016

Use of optical spacers to enhance infrared Mueller ellipsometry sensitivity: application to the characterization of organic thin films.

Appl Opt 2016 Apr;55(12):3323-32

Mueller ellipsometry in the mid-infrared (IR) spectral range can be used to obtain information about chemical composition through the vibrational spectra of samples. In the case of very thin films (<100  nm), the ellipsometric spectral features due to vibrational absorption are in general quite weak, and sometimes they are hidden by the noise in the measured data. In this work, we present one method based on the use of optical spacers as a tool to enhance the sensitivity of IR Mueller ellipsometry. An optical spacer is a thin film made of a known material which is between the substrate and the layer of interest. We show that, when the thickness of the two layers fulfills a given condition, the spectral features due to vibrational absorptions are enhanced. We explain the enhancement effect in terms of the Airy formula. The theoretical discussion is illustrated with two examples. We analyzed polystyrene thin films deposited on silicon wafers. Some of the wafers were covered by a thin film of thermal silicon dioxide (SiO2), which was used as a spacer. The results show the suitability of the proposed technique to overcome the lack of sensitivity in ellipsometric measurements when it comes to working with either very thin films or materials with low absorption.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/AO.55.003323DOI Listing
April 2016

Inline digital holographic movie based on a double-sideband filter.

Opt Lett 2015 Sep;40(17):4142-5

This Letter proposes a new optical architecture based on a double-sideband filter, simultaneously applied at the Fourier plane, for inline digital holography. The proposed architecture not only allows removal of the conjugate images in the reconstruction process but also reduces the distortions that usually appear when using a single-sideband filter. We first introduce the mathematical model that explains the method and then describe the optical setup used for the implementation. The optical system includes a parallel aligned liquid crystal display placed at the Fourier plane that simultaneously filters positive and negative frequencies, when properly combined with linear polarizers. This feature makes the device useful to register dynamic processes. Finally, we tested the setup by registering a holographic movie of microscopic moving objects placed at different planes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OL.40.004142DOI Listing
September 2015

Arbitrary state of polarization with customized degree of polarization generator.

Opt Lett 2015 Aug;40(16):3790-3

An optical setup able to generate arbitrary states of polarization (SOPs) with customized degree of polarization is presented in this Letter. Compared with the few alternatives existing in literature, it presents an easy-to-build optical setup and leads to a superior performance. In fact, experimental results are presented, providing an accurate control for the generation of SOPs (maximum error of 1.7% and 3.3% for ellipticity and azimuth, respectively) as well as for the associated degree of polarization (full experimental variation from 1 up to 0.003, with a 1.7% maximum error). The system proposed may be useful for different applications, for example, for polarimeters testing, speckle metrology, and biological applications.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OL.40.003790DOI Listing
August 2015

Optimization, tolerance analysis and implementation of a Stokes polarimeter based on the conical refraction phenomenon.

Opt Express 2015 Mar;23(5):5636-52

Recently, we introduced the basic concepts behind a new polarimeter device based on conical refraction (CR), which presents several appealing features compared to standard polarimeters. To name some of them, CR polarimeters retrieve the polarization state of an input light beam with a snapshot measurement, allow for substantially enhancing the data redundancy without increasing the measuring time, and avoid instrumental errors owing to rotating elements or phase-to-voltage calibration typical from dynamic devices. In this article, we present a comprehensive study of the optimization, robustness and parameters tolerance of CR based polarimeters. In addition, a particular CR based polarimetric architecture is experimentally implemented, and some concerns and recommendations are provided. Finally, the implemented polarimeter is experimentally tested by measuring different states of polarization, including fully and partially polarized light.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OE.23.005636DOI Listing
March 2015

Use of ferroelectric liquid crystal panels to control state and degree of polarization in light beams.

Opt Lett 2014 Feb;39(3):659-62

We propose a new technique that is able to generate a light beam with a controlled state of polarization (SoP) and a customized degree of polarization (DoP). The technique relies on the fact that effective depolarization can be achieved by temporally averaging a time-dependent SoP. Our proposed setup is based on a ferroelectric liquid crystal panel of retardance λ/2, with a fast polarization switching capability (33 Hz). A mathematical basis describing the experiment is given. In addition, simulation data is discussed, showing the possibility of generating any SoP with full control of the DoP. Finally, to prove the potential of the invention proposed, experimental results are provided as well, reaching an experimental minimum DoP of 0.14.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OL.39.000659DOI Listing
February 2014

Conical refraction as a tool for polarization metrology.

Opt Lett 2013 Oct;38(20):4100-3

A method for polarization metrology based on the conical refraction (CR) phenomenon, occurring in biaxial crystals, is reported. CR transforms an input Gaussian beam into a light ring whose intensity distribution is linked to the incoming polarization. We present the design of a division-of-amplitude complete polarimeter composed of two biaxial crystals, whose measurement principle is based on the CR phenomenon. This design corresponds to a static polarimeter, that is, without mechanical movements or electrical signal addressing. Only one division-of-amplitude device is required, besides the two biaxial crystals, to completely characterize any state of polarization, including partially polarized and unpolarized states. In addition, a mathematical model describing the system is included. Experimental images of the intensity distribution related to different input polarization states are provided. These intensity patterns are compared with simulated values, proving the potential of polarimeters based on biaxial crystals.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OL.38.004100DOI Listing
October 2013

Optimization and tolerance analysis of a polarimeter with ferroelectric liquid crystals.

Appl Opt 2013 Aug;52(23):5748-57

Department of Physics, Universitat Autònoma de Barcelona, Bellaterra, Spain.

We present the design of Stokes and Mueller polarimeters based on ferroelectric liquid crystal (FLC) panels. The instrument is complete and takes time-sequential measurements. A FLC device is modeled as a uniaxial birefringent waveplate with two stable optical axis orientations switchable by a squared electrical signal. The optical parameters of the LC device (retardance and the two stable orientations of the fast axis) are calibrated. Then the orientations of the optical elements of the setup are optimized in order to minimize the propagation of the noise. We also provide a tolerance study to achieve 2% accuracy for the Stokes vector and Mueller matrix metrology. These analyses are conducted as a function of the incident state of polarization and of the Mueller matrix to be measured, respectively. The optimized system is implemented and calibrated in the laboratory. We evaluate its repeatability over 24 h of operation, and the dependence with the temperature is discussed. In addition, we include a study related to the speed of taking the measurements. Finally, we provide some experimental measurements of different Stokes vectors and Mueller matrices, validating the proposed prototypes.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/AO.52.005748DOI Listing
August 2013

Optimized Stokes polarimeters based on a single twisted nematic liquid-crystal device for the minimization of noise propagation.

Appl Opt 2011 Oct;50(28):5437-45

Departamento de Física, Universitat Autònoma de Barcelona, Bellatera, Spain.

This work evidences the suitability of applying a single twisted nematic liquid-crystal (TN-LC) device to obtain dynamic polarimeters with high accuracy and repeatability. Different Stokes polarimeter setups based on a TN-LC device are optimized, leading to the minimization of the noise propagated from intensity measurements to the Stokes vector calculations. To this aim, we revise the influence of working out of normal incidence and of performing a double pass of the light beam through the LC device. In addition, because transmissive TN-LC devices act as elliptical retarders, an extra study is performed. It analyzes the influence of projecting the light exiting from the TN-LC device over elliptical states of polarization. Finally, diverse optimized polarimeters are experimentally implemented and validated by measuring different states of partially and fully polarized light. The analysis is conducted both for monochromatic (He-Ne laser) and LED light sources, proving the potential of polarimeters based on a single TN-LC device.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/AO.50.005437DOI Listing
October 2011

Optimization and performance criteria of a Stokes polarimeter based on two variable retarders.

Opt Express 2010 May;18(10):9815-30

Department of Physics, Universitat Autònoma de Barcelona, 08193, Bellaterra, SPAIN.

In this paper we present the analysis, optimization and implementation of several Stokes polarimeter configurations based on a set-up including two variable retarders. The polarimeter analysis is based on the Mueller-Stokes formalism, and as a consequence, it is suitable to deal with depolarized light. Complete Stokes polarimeters are optimized by minimizing the amplification of simulated errors into the final solution. Different indicators useful to achieve this aim, as the condition number or the equally weighted variance, are compared in this paper. Moreover, some of the optimized polarimeters are experimentally implemented and it is studied the influence of small deviations from the theoretical ones on the amplification of the Stokes component error. In addition, the benefit of using incomplete polarimeters, when detecting specific ranges of states of polarization, is discussed.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/OE.18.009815DOI Listing
May 2010

Time-resolved Mueller matrix analysis of a liquid crystal on silicon display.

Appl Opt 2008 Aug;47(23):4267-74

Departamento de Física, Universidad Autónoma de Barcelona, 08193 Bellaterra, Spain.

We present a full polarimetric characterization of a liquid crystal on silicon (LCoS) display, with time resolution measurements below the frame period of the device. This time-resolved analysis shows evidence of temporal fluctuations in the millisecond range in the state of polarization of the beam reflected by the display. We demonstrate that light reflected by the display is maintained fully polarized, but these temporal fluctuations result in an effective depolarization effect when detectors with long time integration intervals are used in the characterization of the display.
View Article and Find Full Text PDF

Download full-text PDF

Source
http://dx.doi.org/10.1364/ao.47.004267DOI Listing
August 2008