École Nationale Supérieure d'Ingénieurs du Mans

We demonstrate that it is possible to study the modal structures of a vibrating object with digitally recorded holograms by use of the time-averaging principle. We investigate the numerical reconstruction from a theoretical point of view, and we show that the numerically reconstructed object from a digital hologram is modulated by the zeroth-order Bessel function. Results of experiments in time-averaged digital holography are presented.

Features offered by the combination of time averaging and digital Fresnel holography are investigated. In particular, we introduce the concept of the zero-crossing phase of Bessel fringes, which allows a highly contrasted determination of the dark fringes in the hologram. We discuss some particularities of the digital reconstruction and show how time-averaged digital holography can be used to study vibration drifts. Experiment results are presented in the case of a loudspeaker under a sinusoidal excitation; digital and analogical holography are also compared.

An algorithm designed for digital color holography is presented. It is based on a filter bank allowing full object reconstruction with a pixel pitch being invariant along each wavelength. Its application to high-resolution simultaneous two-wavelength metrology is described.

We discuss a method to record and reconstruct color holograms by using a stack of photodiode sensors associated to a one-way reference beam. The reconstruction algorithm follows a convolution strategy in which a transverse magnification leads to the full reconstruction of the object in the reconstructed horizon. The transverse magnification of the object depends on the curvature of the reference wave. Analysis of the spatial resolution indicates that it is linked to the transversal magnification but that no extra information is gained or lost in the process. Experimental results confirm the validity of the proposed approach for two-color digital holography. The error due to spectral mixing is investigated and found to be quite irrelevant compared to the range of the phase measurement.

A biosensor (LUMISENS I), based on the inducible bioluminescence of the Escherichia coli strain TBT3 (Ec::luxAB TBT3), was developed for the detection of the biocide tributyltin. LUMISENS I was set up with a minibioreactor and additional equipment for growth monitoring and light acquisition. The 100-mL minibioreactor has allowed us to establish a stable and reproducible environment for the bacteria (regulation of the growth rate, temperature, pH, and oxygenation), as well as for in situ contact with the xenobiotic. The optical components of the transducer were chosen according to the spectral emission of the strain being studied using a highly sensitive spectrophotometer that was initially devoted to Raman scattering. LUMISENS I was patented according to the in situ, automatic, and simultaneous measurement of the cell density and bioluminescence in the bioreactor. The first results showed that cells cultivated in a synthetic glucose medium provided a better detection limit than did those cultivated in a complex Luria-Bertani (LB) medium (0.02 and 1.5 microM of tributyltin, respectively). Cells maintained at a high growth rate (0.9 h(-1)) led to maximum bioluminescence. Moreover, air bubbling was efficient enough to provide suitable quantities of oxygen for both growth and light emission. When the TBT3 strain used the luxAB genes on its own, decanal, a long-chain aldehyde, had to be added to obtain the bioluminescence reaction. We found that the continuous addition of decanal was the most effective means of obtaining this reaction. The monitoring of the bioluminescence after tributyltin induction showed that the aldehyde was not toxic up to 300 microM during a 7-day experiment. Measurement of tributyltin with LUMISENS I was performed, which showed significant response up to 0.125 microM without any effect on optical density. Even though optimization of the performance of LUMISENS I is still under development, because of its original design, this biosensor is already in use as a warning system for the online monitoring of tributyltin.

We designed and fabricated an electrooptic transverse magnetic-transverse electric mode converter with phase mismatch control integrated in AlGaAs-GaAs. The electrode scheme, which is reported for the first time in such a device, insures a high polarization conversion efficiency with low-driving voltages.

Abstract Within the framework of the detection of toxic substances using specific bacteria, the effect of the toxic chemical compound tributyltin chloride (TBT) on the bacterium Escherichia coli TBT3 was investigated using a noninvasive approach based on micro‐Raman spectroscopy. Various cellular densities with optical density (OD) ranging from 1 to 4 and harvested at different growth phases were induced for 1 h with different TBT concentrations: 1, 3, 5, and 10 µM. As an original contribution, the Raman results show that, in these conditions, the vibrational signatures of bacteria were affected by the presence of the toxic TBT compound, mainly in the signal characteristics from carbohydrates and lipids. Hierarchical cluster analysis (HCA) carried out on the Raman data in these regions makes it possible to classify the spectra in three groups according to the TBT concentration, confirming the progressive influence of the chemical pollutant on the bacterium. This work shows the potentiality for the Raman technique on this subject, even though a low detection threshold corresponding with a concentration of 1 µM of TBT was established.

In this work, we undertook a comparative study of the dynamic dielectric analysis of two unidirectional epoxy composites: flax‐fiber‐reinforced epoxy and flax/carbon‐fiber‐reinforced epoxy (FCFRE). In both composites, three relaxation processes were identified. The first one is the water dipoles polarization imputed to the presence of polar water molecules in flax fiber. The second relaxation process associated with conductivity occurs as a result of the carriers charges diffusion noted for high temperature above glass transition and low frequencies. As for the third dielectric relaxation associated with the interfacial polarization effect is attributable to the accumulation of charges at the fibers/matrix interface. The presence of two carbon plies in the reinforcement gives rise to two interfacial polarization effects in the FCFRE composite. The analysis of the Maxwell–Wagner–Sillars and the water dipoles polarizations using the Havriliak–Negami model revealed that the presence of two plies of carbon can locally decrease the adhesion of flax fibers in the matrix. This analysis was supported by the thermal properties using a differential scanning calorimety and the mechanical properties using a short beam shear test. POLYM. COMPOS., 241–253, 2016. © 2014 Society of Plastics Engineers

A simple technique for measuring the random noise of an interferometric measurement is presented. The method is based on a filtering technique and the use of a low-pass convolution kernel. It is shown that the method gives a deterministic fraction of the real noise present in the experimental data. The evaluation of the probability density allows the determination of the enlarging constant for specifying the confidence level. Experimental results are reported in the case of moderately noisy and significantly noisy interferometric techniques: phase shifting interferometric testing of smooth surfaces and phase shifting speckle interferometry.

This paper proposes a theoretical and experimental analysis of the saturation effect in digital Fresnel holography and generalizes the linear image formulation to the case of the non linear pixel saturation.

The method of digital holography wavefront reconstruction with adjustable magnification is introduced. Since there is strong zero-order diffraction interference on the reconstruction plane, three different methods are proposed to eliminate zero-order diffraction interference, and compared through experiment. The experimental results demonstrated that the mean subtracted from a hologram is an effective method.

The presence of speckle noise and dislocations makes phase restoration potentially difficult in quantitative phase imaging and metrology. Unfortunately, there is no appropriate approach to deal with phase data corrupted by high speckle noise and phase dislocations. Usually, processing schemes may deal with low-pass phase filtering, phase unwrapping, or phase inpainting. This paper discusses the efficient processing to deal with noisy phase maps corrupted with phase dislocations. Six processing schemes, combining four operations, are evaluated. The investigation is carried out by realistic numerical simulations in which strong decorrelation phase noise and phase dislocations are generated. As a result, most robust and faster processing is established. The applicability of the optimal scheme is demonstrated through deformation measurement in dental materials.

An investigation of subjective quality of 16 numerical speckle denoising filter techniques for computer-generated holograms of macroscopic objects with diffuse surfaces is undertaken. Promising candidates with respect to computational complexity and quality are emphasized.

This paper proposes a review of the different opportunities described in literature for quantitative assessment of natural and reconstructed teeth using optical methods. These experimental method are particularly interesting for understanding the behavior of the natural tooth, but even more so for the CAD/CAM (Computerized aided design and computerized aided manufacturing) bonded ceramics reconstructions. Indeed CAD/CAM ceramics are increasingly used as therapeutic options. However, little is known about their mechanical behavior under stress, as the response of the prepared tooth supporting it. In the past years, optical approaches were proposed to get whole field and quantitative measurement of their mechanical properties. This paper discusses the main methods described in literature, as photo elasticity, digital Moiré interferometry, speckle interferometry and digital color holography.

This paper presents a detailed analysis of figures of merit to compare digital Fresnel holography and speckle interferometry. The analysis is based on both theoretical and experimental analyses. A theoretical analysis of the influence of the aperture and lens in the case of speckle interferometry is developed. Compared to digital Fresnel holography, this element is a critical point influencing Shannon conditions, spatial resolution, spatial filtering and photometric efficiency. Optimal filtering and image recovering conditions are thus established. The theoretical analysis is validated by experimental results. The influence of the speckle decorrelation is estimated for the measurement of mechanical deformations. The same mechanical loading has been applied for both experimental configurations. The probability density of the noise map is then estimated. Fitting the curves along the theoretical analysis results in an objective comparison of the decorrelation degrees, and gives keys to compare the decorrelation sensitivity of the methods.

This paper presents a theoretical and experimental comparison between digital Fresnel holography and digital image-plane holography. The role of the aperture diaphragm in image-plane holography is highlighted and figures of merit such as spatial resolution and sensitivity to decorrelation noise are discussed.

This paper proposes a three-color holographic interferometer devoted to the deformation analysis of a composite material submitted to a short beam shear test. The simultaneous recording of three laser wavelengths using a triple CCD sensor results in the evaluation of shear strains at the lateral surface of the sample. Such an evaluation provides a pertinent parameter to detect premature crack in the structure, long before it becomes visible on the real time stress/strain curve, or with a classical microscope.

This paper proposes a first attempt to visualize and analyze the vibrations induced by a bone-conduction device and propagating at the surface of a human skin. The method suggested is based on a so-called “quasi-time-averaging regime” resulting in the retrieval of the vibration amplitude and phase from a sequence of digital Fresnel holograms, recorded with a high image rate.

This paper presents a reconstruction algorithm based on an intermediate digital hologram which leads to the reconstruction of the image of the object with a controlled sampling pitch and number of pixels. The final image is obtained by calculating the diffraction from the intermediate hologram plane to the image plane using the convolution approach. Experimental results confirm the suitability of the proposed method. The calculation time is slightly better than the other similar approaches. Application in digital color holographic imaging shows that the proposed algorithm provides full color images of colored objects.

This paper proposes a processing method for full-field vibrometry based on digital on-line holography at 100kHz. We demonstrate that 20nm vibrations at 17kHz can be measured over large field of view (~500cm2).