Fabrice Pellen

Scattering through fruits during ripening: laser speckle technique correlated to biochemical and fluorescence measurements

This paper reports monitoring fruits maturation using speckle technique. Performed measurements aim the assessing of biological inner fruit variation effect on the speckle image. We show that the speckle grain size is both affected by the glucose level inside the fruits and by the chlorophyll content. Moreover, the determination of circular polarization degree and circular grain size indicate that a Rayleigh diffusion regime gradually becomes predominant in fruits. Principal component analysis is used to highlight high correlation between results and strengthen the establishment of speckle as a novel non invasive method to monitor fruits ripening.

Detection of Golden apples’ climacteric peak by laser biospeckle measurements

In this paper, we report a study in which a laser biospeckle technique is used to detect the climacteric peak indicating the optimal ripeness of fruits. We monitor two batches of harvested Golden apples going through the ripening phase in low- and room-temperature environments, determine speckle parameters, and measure the emitted ethylene concentration using gas chromatography as reference method. Speckle results are then correlated to the emitted ethylene concentration by a principal component analysis. From a practical point of view, this approach allows us to validate biospeckle as a noninvasive and alternative method to respiration rate and ethylene production for climacteric peak detection as a ripening index.

Detection of an underwater target through modulated lidar experiments at grazing incidence in a deep wave basin

The effectiveness of a pulsed radiofrequency modulated lidar and associated processing for underwater target detection at grazing incidence was experimentally assessed in a wave basin 50 m long and 20 m deep, under different conditions of swell produced within this facility to benefit from a controlled interface. This paper reports our experiments and offline data processing results, and describes significant improvements in the probability of detection that demonstrate the interest of using such a technique in this context.

Retrieving controlled motion parameters using two speckle pattern analysis techniques: spatiotemporal correlation and the temporal history speckle pattern

This paper presents simulation of speckle activity through controlling a moving plate. We present two procedures to extract the initial movement frequency and amplitude, either through correlation calculus or through processing the temporal history of the speckle pattern. We compare and discuss these two methods in terms of efficiency and the ability to retrieve motion parameters. The correlation technique seems to be more suitable for monitoring biospeckle activity as it provides more reliable parameter estimation than the temporal history of the speckle pattern. The evolution of temporal history of the speckle pattern parameters and their response sensibility with amplitude and frequency variations have been studied and quantified. Briers contrast appears to depend only on movement amplitude, whereas inertia moment varies with amplitude and frequency.

Experimentally based simulations on modulated lidar for shallow underwater target detection and localization

Light detection and ranging (LIDAR) is currently used for bathymetric measurement or underwater target detection. A new underwater-target detection scheme named modulated lidar was recently proposed. The study reported here deals with optimization of the modulation process to be applied under such detection conditions. A theoretical model was extracted from available experimental results by deconvolution and further used to simulate realistic backscattered signals for the development of a new modulation scheme. Then, an optimum set of amplitude modulation code parameters was obtained by maximizing the target signal-to-noise ratio. This paper will highlight some particularly promising waveform configurations.

Influence of size, proportion, and absorption coefficient of spherical scatterers on the degree of light polarization and the grain size of speckle pattern

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.

Early diagnosis of teeth erosion using polarized laser speckle imaging

Abstract. 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.

Optimization of a dual-rotating-retarder polarimeter designed for hyper-Rayleigh scattering

Hyper-Rayleigh scattering is frequently used to determine all of the rotational invariants of the first hyperpolarizability tensor. It requires numerous polarization states of both incident and scattered light and thus justifies the use of a dual-rotating-retarder polarimeter. We optimized our experimental setup by reducing the condition number of the polarization processing matrix. Our numerical study showed that, on condition to make six measurements, the choice of the detector angle and of the angular steps of both retarders was paramount. Overspecifying the calculation through a much higher number of measurements allowed us to make broad optimal detector angles and retarder angular steps available. Numerical simulations are presented to optimize our experimental setup.

Radiofrequency modulation on optical carrier for target detection enhancement in seawater

The sensitivity of a LIDAR system and the contrast of immersed targets are strongly reduced by the volume backscattering clutter. To overcome this problem it has been suggested to use a radio-frequency modulation in association with an optical carrier at 532 nm; using a pulse laser source will allow one to keep the benefits of the reduction of volume backscattering clutter. Such a technique improves the detection of underwater targets and is justified by the low-pass transfer function shown by sea-water in backscattering configuration.

Evaluation of low viscosity variations in fluids using temporal and spatial analysis of the speckle pattern

The noninvasive detection of a materials 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 materials 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.