Guy Le Brun - Academia.edu (original) (raw)

Papers by Guy Le Brun

Optics Letters, 2016

The noninvasive detection of a material&a... more The noninvasive detection of a material's viscoelasticity is of great importance in the medical field. In fact, certain diseases cause changes in tissue structure and biological fluid viscosity; tracking those changes allows for detection of these diseases. Rheological measurements are also imperative in the industrial field, where it is necessary to characterize a material's viscoelasticity for manufacturing purposes. In this Letter, we present a noncontact, noninvasive, and low cost method for determining low viscosity values and variations in fluids. Laser speckle and viscometric measurements are performed on test samples having low scattering coefficients and low viscosities. The speckle spatial analysis proved to be as accurate as the speckle temporal correlation method reported in previous studies. Very low viscosities of the order of 1 mPa.s were retrieved for the first time using speckle images with either a frame rate of 1950 fps or a single acquired image.

Applied Optics, 2015

In this paper, we present the evolution of speckle pattern polarimetric parameters in response to... more In this paper, we present the evolution of speckle pattern polarimetric parameters in response to controlled changes in scatterer sizes, proportions, and the absorption coefficient in media. The experimental study was performed on mixtures of polystyrene microspheres with dye in order to ensure biological medium-like properties. The speckle grain sizes and degrees of polarization for linear and circular light were monitored. We observed helicity flipping in the degree of circular polarization for small scatterer proportion around 25%. Furthermore, linear depolarization decreased slightly for media containing more small particles. Good agreement was shown with numerical results computed using a Monte Carlo simulation of polarized light taking into account our experimental configuration. Speckle grain size also evolves with the increase of small scatterers as well as the media absorption coefficient. Such variations of properties are encountered during fruit maturation, in tissues in precancerous stages, and any transformation that causes a modification in particle proportions and absorption coefficient in biological media. The computed parameters proved to be sensitive to these changes.

Journal of Biomedical Optics, 2015

Dental erosion starts with a chemical attack on dental tissue causing tooth demineralization, alt... more Dental erosion starts with a chemical attack on dental tissue causing tooth demineralization, altering the tooth structure and making it more sensitive to mechanical erosion. Medical diagnosis of dental erosion is commonly achieved through a visual inspection by the dentist during dental checkups and is therefore highly dependent on the operator's experience. The detection of this disease at preliminary stages is important since, once the damage is done, cares become more complicated. We investigate the difference in light-scattering properties between healthy and eroded teeth. A change in light-scattering properties is observed and a transition from volume to surface backscattering is detected by means of polarized laser speckle imaging as teeth undergo acid etching, suggesting an increase in enamel surface roughness.

Optics Communications, 2007

Conference Digest. 2000 Conference on Lasers and Electro-Optics Europe (Cat. No.00TH8505), 2000

ABSTRACT Summary form only given. Finding an accurate and simple methodology to map the deep-sea ... more ABSTRACT Summary form only given. Finding an accurate and simple methodology to map the deep-sea macroalgae in the West Channel and West Brittany zones are of high interest to evaluate and survey the ecological and economical diversity of the seabed. Nowadays, only emerged or shallow-water macroalgae can be efficiently monitored by passive teledetection techniques based on the spectral analysis of their reflectance, whereas the deep-sea macroalgae are shaded by the water surface. This has led us to propose an in situ monitoring of the seabed using an active spectral methodology based on fluorescence imaging

SPECKLE 2015: VI International Conference on Speckle Metrology, 2015

SPECKLE 2015: VI International Conference on Speckle Metrology, 2015

Optics Communications, 2013

ABSTRACT This study deals with the polarimetric characterization of biological tissues based on t... more ABSTRACT This study deals with the polarimetric characterization of biological tissues based on the Stokes–Mueller formalism. The optimal experimental conditions to study irradiated pig skin samples are analyzed. Two Mueller matrix decomposition techniques, the one developed by Lu and Chipman and the other by Ossikovski, are used. These decompositions allow identification of useful factors such as retardance, diattenuation and depolarization for differentiating between various levels of irradiation and for better interpreting the behavior of the skin with respect to irradiation.

Applied Optics, 2015

ABSTRACT In this paper, we report experimental results where laser speckle grain size and degree ... more ABSTRACT In this paper, we report experimental results where laser speckle grain size and degree of light polarization are used to distinguish different sizes of Bacillus thuringiensis spherical crystals and different concentration within fermentation products. Three strains of Bacillus thuringiensis, isolated from the Lebanese soil, are selected. After fermentation, crystals and spores are separated using a technique based on flotation in order to obtain large quantities of relatively pure crystals. Crystals are then embedded in an agarose matrix gel and illuminated by a laser. Speckle patterns are recorded and analyzed. Results show that when crystals concentrations increase in the sample, the values of light linear polarization degree and speckle grain size decrease, and the negative values of light circular polarization degree increase. A transition from a Rayleigh scattering regime to a Mie regime is also observed. Furthermore, when the diameter of spherical crystal increases, the normalized value of light linear polarization degree and the grain size diminish drastically for a given concentration of crystals in the matrix, whereas the normalized value of light circular polarization degree increases. This optical characterization constitutes an unambiguous signature of spherical crystals produced by fermentations of different Bacillus thuringiensis strains and shows that speckle may potentially be used at an industrial scale as a low-cost and non-invasive technique in order to characterize crystals geometry and to evaluate the yield of crystal production within fermentation.

Detection and Remediation Technologies for Mines and Minelike Targets II, 1997

ABSTRACT Detecting and identifying targets immersed in draught zone are necessary for a safe navi... more ABSTRACT Detecting and identifying targets immersed in draught zone are necessary for a safe navigation. But with today technologies it is very difficult to do it from a ship. Nowadays, this detection still stays a challenge, because sonars are inefficient in the zone just under the waterline. In our laboratory we succeeded in using lidar as a complementary tool of the sonar. With optical detection, active imagery, various immersed targets were detected, identified and classified according to a Mueller matrix and whatever the perturbations on the sea surface and the wind conditions. The possibility of using a particular polarimetric codage with optical signal is discussed in this paper. The aim was to demonstrate that our lidar tool can be improved by choosing the best polarimetric couple in emission and detection. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints

Optics express, Jan 27, 2005

This report about backscattering measure-ments of the speckle produced by strongly-scattering liq... more This report about backscattering measure-ments of the speckle produced by strongly-scattering liquid media shows that the size of the backscattered speckle depends on scattering and anisotropy coefficients. These measurements were aimed at assessing the effects of polarization characteristics of the incident laser beam and of the scattered light on speckle size. The samples under study consisted of monodisperse polystyrene microspheres in solutions, mixtures of different sized-microspheres, milk, blood and pig skin. Such measurements of speckle size in polarization give information on strongly scattering media, allow their discrimination and enable one to characterize the undergone changes.

Speckle06: Speckles, From Grains to Flowers, 2006

ABSTRACT The investigation of the speckle fields obtained from biological fluids or tissues, can ... more ABSTRACT The investigation of the speckle fields obtained from biological fluids or tissues, can be used in medical applications, as an experimental non invasive method to get informations using low cost and low energy lasers. We give a few examples concerning the application of speckle and polarization analysis in the investigation of blood coagulation, platelets aggregation and deterioration of skin by gamma radiation.

Polarization and Remote Sensing, 1992

ABSTRACT Polarimetry has become an indispensable analysis tool, in remote sensing as well as in r... more ABSTRACT Polarimetry has become an indispensable analysis tool, in remote sensing as well as in radar metrology. In the same way, it is possible to characterize immersed targets illuminated by a laser beam, by using signal polarization. Here our purpose is to discriminate them in relation with their depolarizing and diffusing properties. Using the Stokes-Mueller formalism and Gil- Bernabeu depolarization criterion, we have synthesized two different types of images from which we build analysis methods. In this paper, we present different results for some characteristic samples.

Applied Optics, 2014

We propose a new decomposition for depolarizing Mueller matrices. This decomposition, which consi... more We propose a new decomposition for depolarizing Mueller matrices. This decomposition, which consists of a product of four basic optical devices (two diattenuators, a retarder, and a depolarizer) is derived from a previous one known as "symmetric decomposition" [J. Opt. Soc. Am. A26, 1109 (2009)10.1364/JOSAA.26.001109JOAOD61084-7529] and makes it easier to interpret polarization properties of Mueller matrices and improves estimation of the extracted parameters. Its application is illustrated by several theoretical and experimental examples.

Optical Coherence Tomography and Coherence Techniques II, 2005

ABSTRACT We report on the use, in an Optical Coherence Tomography system, of a shaker with a freq... more ABSTRACT We report on the use, in an Optical Coherence Tomography system, of a shaker with a frequency-modulated driving waveform to avoid non-linearities. The device permits to modulate the interferometric signal simply by the displacing the shaker and to recover the OCT signal in depth.

Speckle 2012: V International Conference on Speckle Metrology, 2012

Thin Solid Films, 2004

Porous silicon materials are currently under intense investigation for optoelectronic application... more Porous silicon materials are currently under intense investigation for optoelectronic applications. Spectroscopic ellipsometry (SE) was used to study the optical properties of layers of composite material composed by porous silicon and disperse red one (a red dye ...

physica status solidi (c), 2005

Optics Letters, 2016

The noninvasive detection of a material&a... more The noninvasive detection of a material's viscoelasticity is of great importance in the medical field. In fact, certain diseases cause changes in tissue structure and biological fluid viscosity; tracking those changes allows for detection of these diseases. Rheological measurements are also imperative in the industrial field, where it is necessary to characterize a material's viscoelasticity for manufacturing purposes. In this Letter, we present a noncontact, noninvasive, and low cost method for determining low viscosity values and variations in fluids. Laser speckle and viscometric measurements are performed on test samples having low scattering coefficients and low viscosities. The speckle spatial analysis proved to be as accurate as the speckle temporal correlation method reported in previous studies. Very low viscosities of the order of 1 mPa.s were retrieved for the first time using speckle images with either a frame rate of 1950 fps or a single acquired image.

Applied Optics, 2015

In this paper, we present the evolution of speckle pattern polarimetric parameters in response to... more In this paper, we present the evolution of speckle pattern polarimetric parameters in response to controlled changes in scatterer sizes, proportions, and the absorption coefficient in media. The experimental study was performed on mixtures of polystyrene microspheres with dye in order to ensure biological medium-like properties. The speckle grain sizes and degrees of polarization for linear and circular light were monitored. We observed helicity flipping in the degree of circular polarization for small scatterer proportion around 25%. Furthermore, linear depolarization decreased slightly for media containing more small particles. Good agreement was shown with numerical results computed using a Monte Carlo simulation of polarized light taking into account our experimental configuration. Speckle grain size also evolves with the increase of small scatterers as well as the media absorption coefficient. Such variations of properties are encountered during fruit maturation, in tissues in precancerous stages, and any transformation that causes a modification in particle proportions and absorption coefficient in biological media. The computed parameters proved to be sensitive to these changes.

Journal of Biomedical Optics, 2015

Dental erosion starts with a chemical attack on dental tissue causing tooth demineralization, alt... more Dental erosion starts with a chemical attack on dental tissue causing tooth demineralization, altering the tooth structure and making it more sensitive to mechanical erosion. Medical diagnosis of dental erosion is commonly achieved through a visual inspection by the dentist during dental checkups and is therefore highly dependent on the operator's experience. The detection of this disease at preliminary stages is important since, once the damage is done, cares become more complicated. We investigate the difference in light-scattering properties between healthy and eroded teeth. A change in light-scattering properties is observed and a transition from volume to surface backscattering is detected by means of polarized laser speckle imaging as teeth undergo acid etching, suggesting an increase in enamel surface roughness.

Optics Communications, 2007

Conference Digest. 2000 Conference on Lasers and Electro-Optics Europe (Cat. No.00TH8505), 2000

ABSTRACT Summary form only given. Finding an accurate and simple methodology to map the deep-sea ... more ABSTRACT Summary form only given. Finding an accurate and simple methodology to map the deep-sea macroalgae in the West Channel and West Brittany zones are of high interest to evaluate and survey the ecological and economical diversity of the seabed. Nowadays, only emerged or shallow-water macroalgae can be efficiently monitored by passive teledetection techniques based on the spectral analysis of their reflectance, whereas the deep-sea macroalgae are shaded by the water surface. This has led us to propose an in situ monitoring of the seabed using an active spectral methodology based on fluorescence imaging

SPECKLE 2015: VI International Conference on Speckle Metrology, 2015

SPECKLE 2015: VI International Conference on Speckle Metrology, 2015

Optics Communications, 2013

ABSTRACT This study deals with the polarimetric characterization of biological tissues based on t... more ABSTRACT This study deals with the polarimetric characterization of biological tissues based on the Stokes–Mueller formalism. The optimal experimental conditions to study irradiated pig skin samples are analyzed. Two Mueller matrix decomposition techniques, the one developed by Lu and Chipman and the other by Ossikovski, are used. These decompositions allow identification of useful factors such as retardance, diattenuation and depolarization for differentiating between various levels of irradiation and for better interpreting the behavior of the skin with respect to irradiation.

Applied Optics, 2015

ABSTRACT In this paper, we report experimental results where laser speckle grain size and degree ... more ABSTRACT In this paper, we report experimental results where laser speckle grain size and degree of light polarization are used to distinguish different sizes of Bacillus thuringiensis spherical crystals and different concentration within fermentation products. Three strains of Bacillus thuringiensis, isolated from the Lebanese soil, are selected. After fermentation, crystals and spores are separated using a technique based on flotation in order to obtain large quantities of relatively pure crystals. Crystals are then embedded in an agarose matrix gel and illuminated by a laser. Speckle patterns are recorded and analyzed. Results show that when crystals concentrations increase in the sample, the values of light linear polarization degree and speckle grain size decrease, and the negative values of light circular polarization degree increase. A transition from a Rayleigh scattering regime to a Mie regime is also observed. Furthermore, when the diameter of spherical crystal increases, the normalized value of light linear polarization degree and the grain size diminish drastically for a given concentration of crystals in the matrix, whereas the normalized value of light circular polarization degree increases. This optical characterization constitutes an unambiguous signature of spherical crystals produced by fermentations of different Bacillus thuringiensis strains and shows that speckle may potentially be used at an industrial scale as a low-cost and non-invasive technique in order to characterize crystals geometry and to evaluate the yield of crystal production within fermentation.

Detection and Remediation Technologies for Mines and Minelike Targets II, 1997

ABSTRACT Detecting and identifying targets immersed in draught zone are necessary for a safe navi... more ABSTRACT Detecting and identifying targets immersed in draught zone are necessary for a safe navigation. But with today technologies it is very difficult to do it from a ship. Nowadays, this detection still stays a challenge, because sonars are inefficient in the zone just under the waterline. In our laboratory we succeeded in using lidar as a complementary tool of the sonar. With optical detection, active imagery, various immersed targets were detected, identified and classified according to a Mueller matrix and whatever the perturbations on the sea surface and the wind conditions. The possibility of using a particular polarimetric codage with optical signal is discussed in this paper. The aim was to demonstrate that our lidar tool can be improved by choosing the best polarimetric couple in emission and detection. Bibtex entry for this abstract Preferred format for this abstract (see Preferences) Find Similar Abstracts: Use: Authors Title Abstract Text Return: Query Results Return items starting with number Query Form Database: Astronomy Physics arXiv e-prints

Optics express, Jan 27, 2005

This report about backscattering measure-ments of the speckle produced by strongly-scattering liq... more This report about backscattering measure-ments of the speckle produced by strongly-scattering liquid media shows that the size of the backscattered speckle depends on scattering and anisotropy coefficients. These measurements were aimed at assessing the effects of polarization characteristics of the incident laser beam and of the scattered light on speckle size. The samples under study consisted of monodisperse polystyrene microspheres in solutions, mixtures of different sized-microspheres, milk, blood and pig skin. Such measurements of speckle size in polarization give information on strongly scattering media, allow their discrimination and enable one to characterize the undergone changes.

Speckle06: Speckles, From Grains to Flowers, 2006

ABSTRACT The investigation of the speckle fields obtained from biological fluids or tissues, can ... more ABSTRACT The investigation of the speckle fields obtained from biological fluids or tissues, can be used in medical applications, as an experimental non invasive method to get informations using low cost and low energy lasers. We give a few examples concerning the application of speckle and polarization analysis in the investigation of blood coagulation, platelets aggregation and deterioration of skin by gamma radiation.

Polarization and Remote Sensing, 1992

ABSTRACT Polarimetry has become an indispensable analysis tool, in remote sensing as well as in r... more ABSTRACT Polarimetry has become an indispensable analysis tool, in remote sensing as well as in radar metrology. In the same way, it is possible to characterize immersed targets illuminated by a laser beam, by using signal polarization. Here our purpose is to discriminate them in relation with their depolarizing and diffusing properties. Using the Stokes-Mueller formalism and Gil- Bernabeu depolarization criterion, we have synthesized two different types of images from which we build analysis methods. In this paper, we present different results for some characteristic samples.

Applied Optics, 2014

We propose a new decomposition for depolarizing Mueller matrices. This decomposition, which consi... more We propose a new decomposition for depolarizing Mueller matrices. This decomposition, which consists of a product of four basic optical devices (two diattenuators, a retarder, and a depolarizer) is derived from a previous one known as "symmetric decomposition" [J. Opt. Soc. Am. A26, 1109 (2009)10.1364/JOSAA.26.001109JOAOD61084-7529] and makes it easier to interpret polarization properties of Mueller matrices and improves estimation of the extracted parameters. Its application is illustrated by several theoretical and experimental examples.

Optical Coherence Tomography and Coherence Techniques II, 2005

ABSTRACT We report on the use, in an Optical Coherence Tomography system, of a shaker with a freq... more ABSTRACT We report on the use, in an Optical Coherence Tomography system, of a shaker with a frequency-modulated driving waveform to avoid non-linearities. The device permits to modulate the interferometric signal simply by the displacing the shaker and to recover the OCT signal in depth.

Speckle 2012: V International Conference on Speckle Metrology, 2012

Thin Solid Films, 2004

Porous silicon materials are currently under intense investigation for optoelectronic application... more Porous silicon materials are currently under intense investigation for optoelectronic applications. Spectroscopic ellipsometry (SE) was used to study the optical properties of layers of composite material composed by porous silicon and disperse red one (a red dye ...

physica status solidi (c), 2005