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Claude Amra

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Dr. Joydip Sengupta

Jogesh Chandra Chaudhuri College (University of Calcutta)

Virginie Boucher

CSIC (Consejo Superior de Investigaciones Científicas-Spanish National Research Council)

Daniele Cangialosi

CSIC (Consejo Superior de Investigaciones Científicas-Spanish National Research Council)

Shaykkh Shahbaawz

Pondicherry university

University of Trento

CHANDRA S PERUGU

Indian Institute of Science

Dr Mudasir Ahmad Lone

University of Nottingham

Anupam Singha Roy

Palacky University, Olomouc

Jyotsna Dutta Majumdar

Indian Institute of Technology Kharagpur

University of Illinois at Chicago

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Papers by Claude Amra

Towards tunable optical filters

Optical Interference Coatings, 2001

Page 1. TOWARDS TUNABLE OPTICAL FILTERS R.Parmentier, F. Lemarchand, M. Cathelinaud, G. Albrand, ... more

Characterization and cleaning control of optical coatings by using a goniometric light scatter instrument with sample imaging ability

The principle of a new scattering measurement system including a mobile lighting and a fixed CCD ... more The principle of a new scattering measurement system including a mobile lighting and a fixed CCD array is described. This new system allows a spatially resolved light scattering characterization. Moreover it is possible to separate localized defects contribution from the local roughness measurement. The comprehensive characterization of optical coatings can be performed with this setup , and some examples will be given.

Mechanisms driving self-organization phenomena in random plasmonic metasurfaces under multipulse femtosecond laser exposure: a multitime scale study

Nanophotonics, Mar 18, 2022

Laser-induced transformations of plasmonic metasurfaces pave the way for controlling their anisot... more Laser-induced transformations of plasmonic metasurfaces pave the way for controlling their anisotropic optical response with a micrometric resolution over large surfaces. Understanding the transient state of matter is crucial to optimize laser processing and reach specific optical properties. This article proposes an experimental and numerical study to follow and explain the diverse irreversible transformations encountered by a random plasmonic metasurface submitted to multiple femtosecond laser pulses at a high repetition rate. A pump-probe spectroscopic imaging setup records pulse after pulse, and with a nanosecond time resolution, the polarized transmission spectra of the plasmonic metasurface, submitted to 50,000 ultrashort laser pulses at 75 kHz. The measurements reveal different regimes, occurring in different ranges of accumulated pulse numbers, where successive self-organized embedded periodic nanostructures with very different periods are observed by post-mortem electron microscopy characterizations. Analyses are carried out; thanks to laserinduced temperature rise simulations and calculations of the mode effective indices that can be guided in the structure. The overall study provides a detailed insight into successive mechanisms leading to shape transformation and self-organization in the system, their respective predominance as a function of the laser-induced temperature relative to the melting temperature of metallic nanoparticles and their kinetics. The article also demonstrates the dependence of the self-organized period on the guidedmode effective index, which approaches a resonance due to system transformation. Such anisotropic plasmonic metasurfaces have a great potential for security printing or data storage, and better understanding their formation opens the way to smart optimization of their properties.

Thermal invisibility based on scattering cancellation and mantle cloaking

Scientific Reports, Apr 30, 2015

We theoretically and numerically analyze thermal invisibility based on the concept of scattering ... more We theoretically and numerically analyze thermal invisibility based on the concept of scattering cancellation and mantle cloaking. We show that a small object can be made completely invisible to heat diffusion waves, by tailoring the heat conductivity of the spherical shell enclosing the object. This means that the thermal scattering from the object is suppressed, and the heat flow outside the object and the cloak made of these spherical shells behaves as if the object is not present. Thermal invisibility may open new vistas in hiding hot spots in infrared thermography, military furtivity, and electronics heating reduction.

Laser-induced thermal effects in optical interference coatings

HAL (Le Centre pour la Communication Scientifique Directe), Oct 3, 2022

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

A New Optical Sensor Based on Laser Speckle and Chemometrics for Precision Agriculture: Application to Sunflower Plant-Breeding

Sensors, Aug 18, 2020

New instruments to characterize vegetation must meet cost constraints while providing accurate in... more New instruments to characterize vegetation must meet cost constraints while providing accurate information. In this paper, we study the potential of a laser speckle system as a low-cost solution for non-destructive phenotyping. The objective is to assess an original approach combining laser speckle with chemometrics to describe scattering and absorption properties of sunflower leaves, related to their chemical composition or internal structure. A laser diode system at two wavelengths 660 nm and 785 nm combined with polarization has been set up to differentiate four sunflower genotypes. REP-ASCA was used as a method to analyze parameters extracted from speckle patterns by reducing sources of measurement error. First findings have shown that measurement errors are mostly due to unwilling residual specular reflections. Moreover, results outlined that the genotype significantly impacts measurements. The variables involved in genotype dissociation are mainly related to scattering properties within the leaf. Moreover, an example of genotype classification using REP-ASCA outcomes is given and classify genotypes with an average error of about 20%. These encouraging results indicate that a laser speckle system is a promising tool to compare sunflower genotypes. Furthermore, an autonomous low-cost sensor based on this approach could be used directly in the field.

Broadband loss-less optical thin-film depolarizing devices

Optics Express, May 8, 2018

For some space applications, sensors are sensitive to light polarization and can only be properly... more For some space applications, sensors are sensitive to light polarization and can only be properly calibrated with non-polarized light. Here we propose new optical devices which allow to depolarize light in a spatial process. These devices are thin film multilayers which exhibit polarimetric phase variations in their plane. A zero spatial polarization degree can be reached with high accuracy in a controlled bandwidth.

Wide-range wavelength and angle resolved light scattering measurement setup

Optics Letters, Apr 21, 2020

Optimization of micro-cavities for huge enhancement patterns in free-space and modal space

We show how to design huge enhancement of emission patterns in multilayer planar micro-cavities. ... more We show how to design huge enhancement of emission patterns in multilayer planar micro-cavities. Optimization is carried out arbitrarily for both the free-space pattern of plane waves and for the modal pattern of guided modes. The energy carried by these patterns is compared for various stacks, and their control is discussed.

$Research paper thumbnail of Anomalous refraction phenomena in a transparent slab$

Anomalous refraction phenomena in a transparent slab

arXiv (Cornell University), Dec 15, 2017

An exact formulation of the propagation of a monochromatic wave packet impinging upon a transpare... more An exact formulation of the propagation of a monochromatic wave packet impinging upon a transparent, homogeneous, isotropic and parallel slab at oblique incidence is presented. Approximate formulas are derived for low divergence Gaussian light beams. These formulas show the presence of anomalous refraction phenomena at any slab thickness, including negative refraction and flat lensing effects, induced by the reflection on the rear face.

Spectral efficiency of engineered thermal cloaks in the frequency regime

arXiv (Cornell University), Sep 10, 2014

We analyse basic thermal cloaks designed via different geometric transforms applied to thermal cl... more We analyse basic thermal cloaks designed via different geometric transforms applied to thermal cloaking. We evaluate quantitatively the efficiency of these heterogeneous anisotropic thermal cloaks through the calculation of the standard deviation of the isotherms. The study addresses the frequency regime and we point out the cloak's spectral efficiencies. We find that all these cloaks have comparable efficiency irrespective of whether or not they have singular conductivity at their inner boundary. However, approximate cloaking with multilayered cloak critically depends upon the homogenization algorithm and a large number of thin layers (at least fifty) is required to reduce substantially the standard deviation of the isotherms.

Thermal concentrator homogenized with solar-shaped mantle

arXiv (Cornell University), Aug 7, 2015

We propose solar-shaped thermal concentrators designed with orthoradial layers and obtained in pr... more We propose solar-shaped thermal concentrators designed with orthoradial layers and obtained in practice through the homogenization of an ideal thermal concentrator. Considering the spectral regime of the heat equation, we quantitatively evaluate at different pulsations the effectiveness of the homogenized concentrators by comparing the thermal flux existing in an ideal concentrator and the thermal flux in an homogenized concentrator. Dependence on the pulsation is shown to be negligible and plotting the effectiveness of the homogenized concentrators as a function of the number of orthoradial layers N , we determine the number of layers needed to achieve a certain effectiveness. Significantly high numbers N (ranging from a hundred to tens of thousands layers) are found highlighting the fact that achieving high effectiveness demands a high level of engineering of the homogenized concentrator.

Provable Phase Retrieval with Mirror Descent

Siam Journal on Imaging Sciences, Jul 14, 2023

Provable Phase retrieval via Mirror Descent

HAL (Le Centre pour la Communication Scientifique Directe), Mar 29, 2022

In this paper, we consider the problem of phase retrieval, which consists of recovering an n-dime... more In this paper, we consider the problem of phase retrieval, which consists of recovering an n-dimensional real vector from the magnitude of its m linear measurements. We propose a mirror descent (or Bregman gradient descent) algorithm based on a wisely chosen Bregman divergence, hence allowing to remove the classical global Lipschitz continuity requirement on the gradient of the non-convex phase retrieval objective to be minimized. We apply the mirror descent for two random measurements: the i.i.d standard Gaussian and those obtained by multiple structured illuminations through Coded Diffraction Patterns (CDP). For the Gaussian case, we show that when the number of measurements m is large enough, then with high probability, for almost all initializers, the algorithm recovers the original vector up to a global sign change. For both measurements, the mirror descent exhibits a local linear convergence behaviour with a dimension-independent convergence rate. Our theoretical results are finally illustrated with various numerical experiments, including an application to the reconstruction of images in precision optics.

Design and manufacture of high absorption metal dielectric coatings for the reduction of straylight

This paper describes the design and manufacture of broadband metal dielectric absorbers. First, w... more This paper describes the design and manufacture of broadband metal dielectric absorbers. First, we give some design principles to obtain achromatic absorption properties. Then, we describe a new method to determine the complex refractive index of metallic layers. A graded index model is developed to take account of the evolution of the film packing density. Manufacturing is detailed in the last section. Absorption levels higher than 99.9% have been measured over the visible range.

Wide angle light scattering and complex optical filters: modelization and characterization

Because of their complexity (>100 layers) and their decreasing dimensions (~pixel size), performa... more Because of their complexity (>100 layers) and their decreasing dimensions (~pixel size), performances of the new generation of optical filters for space application are degraded by wide angle light scattering. For these reasons, it is huge important to be able to predict and measure the angular and specral behaviour of light scattered by complex interferential filters. In this paper, light scattering is calculated for complex filters and take simultaneously account of most parameters: surface roughness, bulk inhomogeneity, cross-correlation coefficients, errors in design, wavelength and scattering angles (normal and polar), polarization… All these variations have become necessary to predict a balance in optical multiplexers and related systems, mainly for space applications. To complete the analysis, a metrological platform dedicated to the multimodal characterization of scattering losses has been involved.

A New Optical Sensor Based on Laser Speckle and Chemometrics for Precision Agriculture: Application to Sunflower Plant-Breeding

Sensors, 2020

New instruments to characterize vegetation must meet cost constraints while providing accurate in... more New instruments to characterize vegetation must meet cost constraints while providing accurate information. In this paper, we study the potential of a laser speckle system as a low-cost solution for non-destructive phenotyping. The objective is to assess an original approach combining laser speckle with chemometrics to describe scattering and absorption properties of sunflower leaves, related to their chemical composition or internal structure. A laser diode system at two wavelengths 660 nm and 785 nm combined with polarization has been set up to differentiate four sunflower genotypes. REP-ASCA was used as a method to analyze parameters extracted from speckle patterns by reducing sources of measurement error. First findings have shown that measurement errors are mostly due to unwilling residual specular reflections. Moreover, results outlined that the genotype significantly impacts measurements. The variables involved in genotype dissociation are mainly related to scattering propert...

Inverse heat mimicking of given objects

Scientific Reports, 2017

We address a general inverse mimicking problem in heat conduction. The objects to cloak and mimic... more We address a general inverse mimicking problem in heat conduction. The objects to cloak and mimic are chosen beforehand; these objects identify a specific set of space transformations. The shapes that can be mimicked are derived from the conductivity matrices. Numerical calculation confirms all of the analytical predictions. The technique provides key advantages for applications and can be extended to the field of waves.

Speckle intensity statistics for chromatic scattering media under partially polarized illumination

Optics Express, 2015

Intensity contrast in a fully developed speckle pattern resulting from the elastic scattering of ... more Intensity contrast in a fully developed speckle pattern resulting from the elastic scattering of a partially polarized light from a strongly scattering medium is theoretically and numerically studied. Simple expressions are derived when the illumination bandwidth is much smaller or larger than the chromatic length of the scattering medium.

Transformed Fourier and Fick equations for the control of heat and mass diffusion

AIP Advances, 2015

We review recent advances in the control of diffusion processes in thermodynamics and life scienc... more We review recent advances in the control of diffusion processes in thermodynamics and life sciences through geometric transforms in the Fourier and Fick equations, which govern heat and mass diffusion, respectively. We propose to further encompass transport properties in the transformed equations, whereby the temperature is governed by a three-dimensional, time-dependent, anisotropic heterogeneous convection-diffusion equation, which is a parabolic partial differential equation combining the diffusion equation and the advection equation. We perform two dimensional finite element computations for cloaks, concentrators and rotators of a complex shape in the transient regime. We precise that in contrast to invisibility cloaks for waves, the temperature (or mass concentration) inside a diffusion cloak crucially depends upon time, its distance from the source, and the diffusivity of the invisibility region. However, heat (or mass) diffusion outside cloaks, concentrators and rotators is u...

Towards tunable optical filters

Optical Interference Coatings, 2001

Page 1. TOWARDS TUNABLE OPTICAL FILTERS R.Parmentier, F. Lemarchand, M. Cathelinaud, G. Albrand, ... more

Characterization and cleaning control of optical coatings by using a goniometric light scatter instrument with sample imaging ability

The principle of a new scattering measurement system including a mobile lighting and a fixed CCD ... more The principle of a new scattering measurement system including a mobile lighting and a fixed CCD array is described. This new system allows a spatially resolved light scattering characterization. Moreover it is possible to separate localized defects contribution from the local roughness measurement. The comprehensive characterization of optical coatings can be performed with this setup , and some examples will be given.

Mechanisms driving self-organization phenomena in random plasmonic metasurfaces under multipulse femtosecond laser exposure: a multitime scale study

Nanophotonics, Mar 18, 2022

Laser-induced transformations of plasmonic metasurfaces pave the way for controlling their anisot... more Laser-induced transformations of plasmonic metasurfaces pave the way for controlling their anisotropic optical response with a micrometric resolution over large surfaces. Understanding the transient state of matter is crucial to optimize laser processing and reach specific optical properties. This article proposes an experimental and numerical study to follow and explain the diverse irreversible transformations encountered by a random plasmonic metasurface submitted to multiple femtosecond laser pulses at a high repetition rate. A pump-probe spectroscopic imaging setup records pulse after pulse, and with a nanosecond time resolution, the polarized transmission spectra of the plasmonic metasurface, submitted to 50,000 ultrashort laser pulses at 75 kHz. The measurements reveal different regimes, occurring in different ranges of accumulated pulse numbers, where successive self-organized embedded periodic nanostructures with very different periods are observed by post-mortem electron microscopy characterizations. Analyses are carried out; thanks to laserinduced temperature rise simulations and calculations of the mode effective indices that can be guided in the structure. The overall study provides a detailed insight into successive mechanisms leading to shape transformation and self-organization in the system, their respective predominance as a function of the laser-induced temperature relative to the melting temperature of metallic nanoparticles and their kinetics. The article also demonstrates the dependence of the self-organized period on the guidedmode effective index, which approaches a resonance due to system transformation. Such anisotropic plasmonic metasurfaces have a great potential for security printing or data storage, and better understanding their formation opens the way to smart optimization of their properties.

Thermal invisibility based on scattering cancellation and mantle cloaking

Scientific Reports, Apr 30, 2015

We theoretically and numerically analyze thermal invisibility based on the concept of scattering ... more We theoretically and numerically analyze thermal invisibility based on the concept of scattering cancellation and mantle cloaking. We show that a small object can be made completely invisible to heat diffusion waves, by tailoring the heat conductivity of the spherical shell enclosing the object. This means that the thermal scattering from the object is suppressed, and the heat flow outside the object and the cloak made of these spherical shells behaves as if the object is not present. Thermal invisibility may open new vistas in hiding hot spots in infrared thermography, military furtivity, and electronics heating reduction.

Laser-induced thermal effects in optical interference coatings

HAL (Le Centre pour la Communication Scientifique Directe), Oct 3, 2022

HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific re... more HAL is a multidisciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

A New Optical Sensor Based on Laser Speckle and Chemometrics for Precision Agriculture: Application to Sunflower Plant-Breeding

Sensors, Aug 18, 2020

New instruments to characterize vegetation must meet cost constraints while providing accurate in... more New instruments to characterize vegetation must meet cost constraints while providing accurate information. In this paper, we study the potential of a laser speckle system as a low-cost solution for non-destructive phenotyping. The objective is to assess an original approach combining laser speckle with chemometrics to describe scattering and absorption properties of sunflower leaves, related to their chemical composition or internal structure. A laser diode system at two wavelengths 660 nm and 785 nm combined with polarization has been set up to differentiate four sunflower genotypes. REP-ASCA was used as a method to analyze parameters extracted from speckle patterns by reducing sources of measurement error. First findings have shown that measurement errors are mostly due to unwilling residual specular reflections. Moreover, results outlined that the genotype significantly impacts measurements. The variables involved in genotype dissociation are mainly related to scattering properties within the leaf. Moreover, an example of genotype classification using REP-ASCA outcomes is given and classify genotypes with an average error of about 20%. These encouraging results indicate that a laser speckle system is a promising tool to compare sunflower genotypes. Furthermore, an autonomous low-cost sensor based on this approach could be used directly in the field.

Broadband loss-less optical thin-film depolarizing devices

Optics Express, May 8, 2018

For some space applications, sensors are sensitive to light polarization and can only be properly... more For some space applications, sensors are sensitive to light polarization and can only be properly calibrated with non-polarized light. Here we propose new optical devices which allow to depolarize light in a spatial process. These devices are thin film multilayers which exhibit polarimetric phase variations in their plane. A zero spatial polarization degree can be reached with high accuracy in a controlled bandwidth.

Wide-range wavelength and angle resolved light scattering measurement setup

Optics Letters, Apr 21, 2020

Optimization of micro-cavities for huge enhancement patterns in free-space and modal space

We show how to design huge enhancement of emission patterns in multilayer planar micro-cavities. ... more We show how to design huge enhancement of emission patterns in multilayer planar micro-cavities. Optimization is carried out arbitrarily for both the free-space pattern of plane waves and for the modal pattern of guided modes. The energy carried by these patterns is compared for various stacks, and their control is discussed.

$Research paper thumbnail of Anomalous refraction phenomena in a transparent slab$

Anomalous refraction phenomena in a transparent slab

arXiv (Cornell University), Dec 15, 2017

An exact formulation of the propagation of a monochromatic wave packet impinging upon a transpare... more An exact formulation of the propagation of a monochromatic wave packet impinging upon a transparent, homogeneous, isotropic and parallel slab at oblique incidence is presented. Approximate formulas are derived for low divergence Gaussian light beams. These formulas show the presence of anomalous refraction phenomena at any slab thickness, including negative refraction and flat lensing effects, induced by the reflection on the rear face.

Spectral efficiency of engineered thermal cloaks in the frequency regime

arXiv (Cornell University), Sep 10, 2014

We analyse basic thermal cloaks designed via different geometric transforms applied to thermal cl... more We analyse basic thermal cloaks designed via different geometric transforms applied to thermal cloaking. We evaluate quantitatively the efficiency of these heterogeneous anisotropic thermal cloaks through the calculation of the standard deviation of the isotherms. The study addresses the frequency regime and we point out the cloak's spectral efficiencies. We find that all these cloaks have comparable efficiency irrespective of whether or not they have singular conductivity at their inner boundary. However, approximate cloaking with multilayered cloak critically depends upon the homogenization algorithm and a large number of thin layers (at least fifty) is required to reduce substantially the standard deviation of the isotherms.

Thermal concentrator homogenized with solar-shaped mantle

arXiv (Cornell University), Aug 7, 2015

We propose solar-shaped thermal concentrators designed with orthoradial layers and obtained in pr... more We propose solar-shaped thermal concentrators designed with orthoradial layers and obtained in practice through the homogenization of an ideal thermal concentrator. Considering the spectral regime of the heat equation, we quantitatively evaluate at different pulsations the effectiveness of the homogenized concentrators by comparing the thermal flux existing in an ideal concentrator and the thermal flux in an homogenized concentrator. Dependence on the pulsation is shown to be negligible and plotting the effectiveness of the homogenized concentrators as a function of the number of orthoradial layers N , we determine the number of layers needed to achieve a certain effectiveness. Significantly high numbers N (ranging from a hundred to tens of thousands layers) are found highlighting the fact that achieving high effectiveness demands a high level of engineering of the homogenized concentrator.

Provable Phase Retrieval with Mirror Descent

Siam Journal on Imaging Sciences, Jul 14, 2023

Provable Phase retrieval via Mirror Descent

HAL (Le Centre pour la Communication Scientifique Directe), Mar 29, 2022

In this paper, we consider the problem of phase retrieval, which consists of recovering an n-dime... more In this paper, we consider the problem of phase retrieval, which consists of recovering an n-dimensional real vector from the magnitude of its m linear measurements. We propose a mirror descent (or Bregman gradient descent) algorithm based on a wisely chosen Bregman divergence, hence allowing to remove the classical global Lipschitz continuity requirement on the gradient of the non-convex phase retrieval objective to be minimized. We apply the mirror descent for two random measurements: the i.i.d standard Gaussian and those obtained by multiple structured illuminations through Coded Diffraction Patterns (CDP). For the Gaussian case, we show that when the number of measurements m is large enough, then with high probability, for almost all initializers, the algorithm recovers the original vector up to a global sign change. For both measurements, the mirror descent exhibits a local linear convergence behaviour with a dimension-independent convergence rate. Our theoretical results are finally illustrated with various numerical experiments, including an application to the reconstruction of images in precision optics.

Design and manufacture of high absorption metal dielectric coatings for the reduction of straylight

This paper describes the design and manufacture of broadband metal dielectric absorbers. First, w... more This paper describes the design and manufacture of broadband metal dielectric absorbers. First, we give some design principles to obtain achromatic absorption properties. Then, we describe a new method to determine the complex refractive index of metallic layers. A graded index model is developed to take account of the evolution of the film packing density. Manufacturing is detailed in the last section. Absorption levels higher than 99.9% have been measured over the visible range.

Wide angle light scattering and complex optical filters: modelization and characterization

Because of their complexity (>100 layers) and their decreasing dimensions (~pixel size), performa... more Because of their complexity (>100 layers) and their decreasing dimensions (~pixel size), performances of the new generation of optical filters for space application are degraded by wide angle light scattering. For these reasons, it is huge important to be able to predict and measure the angular and specral behaviour of light scattered by complex interferential filters. In this paper, light scattering is calculated for complex filters and take simultaneously account of most parameters: surface roughness, bulk inhomogeneity, cross-correlation coefficients, errors in design, wavelength and scattering angles (normal and polar), polarization… All these variations have become necessary to predict a balance in optical multiplexers and related systems, mainly for space applications. To complete the analysis, a metrological platform dedicated to the multimodal characterization of scattering losses has been involved.

A New Optical Sensor Based on Laser Speckle and Chemometrics for Precision Agriculture: Application to Sunflower Plant-Breeding

Sensors, 2020

New instruments to characterize vegetation must meet cost constraints while providing accurate in... more New instruments to characterize vegetation must meet cost constraints while providing accurate information. In this paper, we study the potential of a laser speckle system as a low-cost solution for non-destructive phenotyping. The objective is to assess an original approach combining laser speckle with chemometrics to describe scattering and absorption properties of sunflower leaves, related to their chemical composition or internal structure. A laser diode system at two wavelengths 660 nm and 785 nm combined with polarization has been set up to differentiate four sunflower genotypes. REP-ASCA was used as a method to analyze parameters extracted from speckle patterns by reducing sources of measurement error. First findings have shown that measurement errors are mostly due to unwilling residual specular reflections. Moreover, results outlined that the genotype significantly impacts measurements. The variables involved in genotype dissociation are mainly related to scattering propert...

Inverse heat mimicking of given objects

Scientific Reports, 2017

We address a general inverse mimicking problem in heat conduction. The objects to cloak and mimic... more We address a general inverse mimicking problem in heat conduction. The objects to cloak and mimic are chosen beforehand; these objects identify a specific set of space transformations. The shapes that can be mimicked are derived from the conductivity matrices. Numerical calculation confirms all of the analytical predictions. The technique provides key advantages for applications and can be extended to the field of waves.

Speckle intensity statistics for chromatic scattering media under partially polarized illumination

Optics Express, 2015

Intensity contrast in a fully developed speckle pattern resulting from the elastic scattering of ... more Intensity contrast in a fully developed speckle pattern resulting from the elastic scattering of a partially polarized light from a strongly scattering medium is theoretically and numerically studied. Simple expressions are derived when the illumination bandwidth is much smaller or larger than the chromatic length of the scattering medium.

Transformed Fourier and Fick equations for the control of heat and mass diffusion

AIP Advances, 2015

We review recent advances in the control of diffusion processes in thermodynamics and life scienc... more We review recent advances in the control of diffusion processes in thermodynamics and life sciences through geometric transforms in the Fourier and Fick equations, which govern heat and mass diffusion, respectively. We propose to further encompass transport properties in the transformed equations, whereby the temperature is governed by a three-dimensional, time-dependent, anisotropic heterogeneous convection-diffusion equation, which is a parabolic partial differential equation combining the diffusion equation and the advection equation. We perform two dimensional finite element computations for cloaks, concentrators and rotators of a complex shape in the transient regime. We precise that in contrast to invisibility cloaks for waves, the temperature (or mass concentration) inside a diffusion cloak crucially depends upon time, its distance from the source, and the diffusivity of the invisibility region. However, heat (or mass) diffusion outside cloaks, concentrators and rotators is u...