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International audience; There is a constant need for direct counting of biotic nanoparticles such as viruses to unravel river functioning. We used, for the first time in freshwater, a new method based on interferometry differentiating viruses from other particles such as membrane vesicles. In the French Marne River, viruses represented between 42 and 72% of the particles. A spring monitoring in 2014 revealed their increase (2.1 × 107 to 2.1 × 108 mL−1) linked to an increase in algal biomass and diversity of bacterial plankton. Predicted virus size distributions were in agreement with transmission electron microscopy analysis suggesting a dominance of large viruses (≥60 nm).

The hypersensitive response has been mostly studied by molecular and biochemical methods after sample destruction. The development of imaging techniques allows the monitoring of physiological changes before any signs of cell death. Here, we follow the early steps of a hypersensitive-like response induced by the bacterial elicitor harpin in Nicotiana sp. We describe cytological modifications after inoculation of the harpin protein, using confocal fluorescence microscopy (CFM) and optical coherence tomography (OCT), an interferometric-based microscopy. The changes detected by CFM occurred 5 h after harpin infiltration and corresponded to a redistribution of the chloroplasts from the upper to the inner regions of the palisade mesophyll cells which could be related to a perturbation in the microtubule network. Using OCT, we were able to detect a decrease in chloroplast backscattered signal as early as 30 min after harpin infiltration. A simple physical model, which accounted for the structure and distribution of thylakoid membranes, suggested that this loss of scattering could be associated with a modification in the refractive index of the thylakoid membranes. Our OCT observations were correlated with a decrease in photosynthesis, emphasizing changes in chloroplast structure as one of the earliest hallmarks of plant hypersensitive cell death.

Summary The establishment of Erwinia amylovora harpin-induced hypersensitive response (HR) in Nicotiana sylvestris was followed by infra-red thermography (IRT). Three to four hours after elicitation, the temperature decreased in the harpin-infiltrated zone associated to stomatal opening. The marked drop in temperature which reached 2°C and preceded necrosis symptoms for several hours, is thus likely caused by higher transpiration. Neither of these effects was observed in a respiratory mutant, affected in complex I structure and function and over-expressing alternative oxidase, indicating that they are directly or indirectly mediated by mitochondrial function. However, as the HR establishment was similar in both wild type and mutant, cell death was either uncorrelated with the observed epidermal changes or occurred by a different signalling pathway in the two genotypes. IRT revealed a novel aspect of plant–pathogen interactions and could be applied to screen for mutants affected in elicitor signalling and/or for respiratory mutants.

Intracellular motion can be quantitatively monitored in tissues using coherence-gated microscopic techniques. With full-field optical coherence tomography (FFOCT), the use of high numerical aperture microscope objectives provides a high resolution mapping of intracellular dynamics that are probed with subwavelength sensitivity. In the upper temporal bandwidth that we have used (1-6 Hz) the main contribution to the dynamic signal arises from the overall dynamical, optically heterogeneous cytoplasm. We propose a method to specifically study the impact of actomyosin contractility on the intracellular dynamic signal by performing high throughput, comparative measurements of multicellular aggregates with and without blebbistatin action, a selective inhibitor of class-II myosins that disrupts actomyosin contractile activity. Our results indicate a significant increase in the fraction of the signal that decorrelates within 1 second after inhibition of contractility. This observation mitigates the anticipated importance of actomyosin contractile forces to directly move organelles, but highlights their role in hindering organelle transport via their stiffening effect of the viscoelastic cytoplasm.

InGaAsP/InP buried heterostructure lasers were investigated using reflectance microscopy. Measurements were performed for both biased (current modulation) and non-biased (modulated pump beam) device. Maps of the facets of non-degraded and degraded lasers are presented and discussed.

We have studied heat diffusion from rough surfaces in different materials exposed to a constant heating and we observed anomalously slow temperature rises over about 3 time decades which indicate a hyperdiffusion phenomenon.

This demonstration of mirage effect under a microscope provides a new possibility to measure the thermal diffusivity of a transparent sample as small as a few microns, with micronic spatial resolution.

We experimentally measure the monochromatic transmission matrix (TM) of an optical multiple scattering medium using a spatial light modulator together with a phase-shifting interferometry measurement method. The TM contains all information needed to shape the scattered output field at will or to detect an image through the medium. We confront theory and experiment for these applications and we study the effect of noise on the reconstruction method. We also extracted from the TM informations about the statistical properties of the medium and the light transport whitin it. In particular, we are able to isolate the contributions of the Memory Effect (ME) and measure its attenuation length.

We report the optical conductivity of YBa 2 Cu 3 O 7 and Bi 2 Sr 2 CaCu 2 O 8+δ thin films at room temperature. The optical conductivity in the 500–7000 cm −1 frequency range is analysed in terms of a frequency dependent relaxation time τ and effective mass of the normal carriers. The relaxation rate 1/τ exhibits the same linear dependence on frequency whatever the sample. The assumption that 1/τ also depends linearly on temperature accounts satisfactorily for the temperature variation (90–300K) of the transmission in the 1000–7000 cm −1 range. These results are consistent with the marginal Fermi liquid model.

International audience; We propose an original adaptive wavefront holographic setup based on the photorefractive effect (PR), to make real-time measurements of acousto-optic signals in thick scattering media, with a high flux collection at high rates for breast tumor detection. We describe here our present state of art and understanding on the problem of breast imaging with PR detection of the acousto-optic signal.

We report experimental evidence and correction of defocus in full-field OCT of biological samples due to mismatch of the refractive index of biological tissues and water. Via a metric based on the image quality, we demonstrate that we are able to compensate this index-induced defocus and to recover a sharp image in depth., 7 pages, 3 figures, minor changes, 1 figure added

International audience; The authors present a method of focusing high intensity ultrasound by time-reversing the photoacoustic response of an optically selective target in a nonselective background. The target’s photoacoustic response was isolated from the background by subtracting the photoacoustic waveforms obtained at different optical wavelengths and convolved with a continuous signal. It was found that the focus produced was comparable in quality to that obtained by delay-law beam-forming. The method holds the promise of allowing precise targeting of high intensity focused ultrasound on nonechogenic targets, in moving environments, independently of the presence of aberrating layers.

International audience; An interferometric method for parallel optical spectroscopy in the kilohertz range is reported, as well as its experimental validation in the context of high speed laser Doppler imaging in vivo. The interferometric approach enables imaging in the low light conditions of a 2 kHz frame rate recording with a complementary metal-oxide semi-conductor (CMOS) camera. Observation of a mice cranium with near infrared ($\lambda$ = 785 nm) laser light in reflection configuration is reported. Doppler spectral images allegedly sensitive to blood flow are measured at several optical frequency detunings sequentially, to shift the spectral range of analysis in the radiofrequency (RF) spectrum.

We present a polarization-sensitive full-field optical coherence tomography system that can produce high-resolution images of the linear retardance and reflectivity properties of biological media. En face images can be delivered at a frame rate of 3.5 Hz by combination of interferometric images acquired by two CCD cameras in an interference microscope illuminated with a tungsten halogen lamp. Isotropic spatial resolution of approximately 1.0 microm is achieved. The technique is demonstrated on ex vivo muscle tissues.

The authors present a camera-based optical detection scheme designed to detect the transient motion created by the acoustic radiation force in soft elastic media. An optically diffusive tissue-mimicking phantom was illuminated with coherent laser light, and a high speed camera (2kHz frame rate) was used to acquire and cross-correlate consecutive speckle patterns. Time-resolved transient decorrelation of the optical speckle was measured as the result of localized motion induced by the radiation force and the associated propagating shear waves. The proposed technique is sensitive only to the low frequency transient motion induced in the medium by the radiation force.

The Virgo interferometer, aimed at detecting gravitational waves, is now in a commissioning phase. Measurements of its optical properties are needed for the understanding of the instrument. We present the techniques developed for the measurement of the optical parameters of Virgo. These parameters are compared with the Virgo specifications.

Imaging below fingertip surface might be a useful alternative to the traditional fingerprint sensing since the internal finger features are more reliable than the external ones. One of the most promising subsurface imaging technique is optical coherence tomography (OCT), which, however, has to acquire 3-D data even when a single en face image is required. This makes OCT inherently slow for en face imaging and produce unnecessary large data sets. Here we demonstrate that full-field optical coherence tomography (FF-OCT) can be used to produce en face images of sweat pores and internal fingerprints, which can be used for the identification purposes.

In this work, the authors use the photoacoustic effect to create a source for ultrasonic time-reversal experiments. Photoacoustic waves were generated by an optically absorbing gel sphere excited by a laser pulse in a highly optically diffusive solution and recorded with an ultrasound array controlled by a time-reversal electronics. The emission of the time-reversed photoacoustic waves allowed the refocusing of the ultrasound towards the optical absorber, in particular, in the presence of a strongly acoustically defocusing medium. The authors illustrate how the technique can be applied to perform acoustical imaging in the presence of a strong acoustical aberration.

We present the new advances in full field optical coherence microscopy, an alternative method to conventional optical coherence tomography (OCT). The experimental setup is based on Linnik interferometer illuminated with a tungsten halogen lamp. En face tomographic images are obtained in real-time without scanning by computing the difference of two phase-opposed interferometric images recorded by a high-resolution CCD camera. The short coherence length of the source and the compensation of dispersion mismatch in the interferometer arms yield an optical sectioning ability with 0.8 μm resolution in water. Transverse resolution of 1.0 μm is achieved by using microscope objectives with a numerical aperture of 0.5. A shot-noise limited detection sensitivity of 86 dB can be reached with 2 s acquisition time. High-resolution images of the anterior segment of the rat eye are shown.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

International audience; A method for measuring birefringence by use of thermal-light polarization-sensitive optical coherence tomography is presented. The use of thermal light brings to polarization-sensitive optical coherence tomography a resolution in the micrometer range in three dimensions. The instrument is based on a Linnik interference microscope and makes use of achromatic quarter-wave plates. A mathematical representation of the instrument is presented here, and the detection scheme is described, together with a discussion of the validity domain of the equations used to evaluate the birefringence in the presence of white-light illumination

International audience; We have built a high-resolution optical coherence tomography (OCT) system, based on a Linnik-type interference microscope, illuminated by a white-light thermal lamp. The extremely short coherence length of the illumination source and the large aperture of the objectives permit resolution close to 1 mm in three dimensions. A parallel detection scheme with a CCD camera provides cross-section x y image acquisition without scanning at a rate of up to 50 Hz. To our knowledge, our system has the highest resolution demonstrated to date for OCT imaging. With identical resolution in three dimensions, realistic volume rendering of structures inside biological tissues is possible.

International audience; We propose to image local defects inside multidielectric optical components by using a special configuration Linnik interference microscope, along with a CCD camera and a dedicated detection, to extract the amplitude scattered by the defects in the interference image. The use of a short coherence length source allows one to obtain interference only from a thin slice (similar to1 mum) within the observed object. The object is tilted to permit the use of a dark-field configuration to enhance the defect contrast. We describe the experimental setup and the detection scheme. Images that exhibit local point defects on the interfaces of various multilayer optical components (laser mirrors) are presented.

An international round robin study was conducted on the absorption measurement of laser-quality coatings. Sets of optically coated samples were made by a reactive DC magnetron sputtering and an ion beam sputtering deposition process. The sample set included a high reflector at 514 nm and a high reflector for the near infrared (1030 to 1318 nm), single layers of silicon dioxide, tantalum pentoxide, and hafnium dioxide. For calibration purposes, a sample metalized with hafnium and an uncoated, superpolished fused silica substrate were also included. The set was sent to laboratory groups for absorptance measurement of these coatings. Whenever possible, each group was to measure a common, central area and another area specifically assigned to the respective group. Specific test protocols were also suggested in regards to the laser exposure time, power density, and surface preparation.

International audience; The interferogram produced by wide-aperture interferometers is studied both theoretically and experimentally. The fringe spacing is shown to increase non linearly with the numerical aperture and the fringe contrast to decrease with the optical path difference. Phase measurements with wide-aperture interferometers therefore require calibration and the phase can be measured only over a limited range. A calibration is given for accurate phase measurements and the range over which the phase can be measured is calculated. Experimental measurements are presented and compared with theory.

Using light to image in‐depth structures and to quantify them in terms of optical (absorption, scattering) properties is a goal for physicists. We will recall the approaches which overcome the strong loss of the photons directional memory in scattering media and their limitations in terms of depth and resolution. Then we will consider hybrid methods which couple acoustics and optics to reach the optical contrast with the acoustic resolution: opto‐acoustics, where a locally absorbed laser pulse generates an acoustic signal whose position and depth can be localized by an array of piezoelectric detectors, and acousto‐optics (A.O.), where an ultrasonic beam modulates the speckle. We will focus on the principle of A.O. signal generation for tagging spatially selected photons and describe various approaches based on numerical heterodyne holography or heterodyne holography using a photo‐refractive beam splitter. To get enough signals through thick tissues (e.g., breast) in a short time we use these techniques at...

We use thermal imaging of Joule heating to see for the first time electrical conducting paths created by the so-called Branly effect in a two-dimensional metallic granular medium (aluminium). Multiple breakdowns are shown to occur when the medium is submitted to high voltage increases (more than 500 V) with rise times close to one hundred of microseconds., 4 pages, 5 figures, related informations at http://chemphys.weizmann.ac.il/~damien/index.html

International audience; Full-Field OCT (FF-OCT) is able to image biological tissues in 3D with micrometer resolution. In this study we add elastographic contrast to the FF-OCT modality. By combining FF-OCT with elastography, we create a “virtual palpation” map at the micrometer scale. We present here a proof of concept on multi-layer phantoms and preliminary results on exvivo biological samples such as porcine cornea, human breast tissues and rat heart. The 3D digital volume correlation that is used in connection with the 3D stack of images allows to access to the full 3D strain tensor and to reveal stiffness anisotropy.

A differential stimulated I.R. detection scheme is presented in order to obtain a better contrast in crack detection on real samples whose surface exhibits topographical and optical irregularities. A finite element simulation confirms the magnitude and shape of the signals for vertical and slanted cracks.

Within the framework of the Virgo project, characterisations of low-absorption high reflectivity multilayers coatings by collinear mirage effect at 1064µm are reported. All the tested samples have absorption losses lower than 20 ppm and the lowest observed average absorption loss is 0.99 ppm.

We propose here to use a neural network as a help in the identification of individual components of a gaz mixture and in the evaluation of the concentration level of each component as they appear in real photoacoustic spectra in presence of background signals and noises. The method is based on the dependance of the activation functions with regard to the input level controled variation and on the desactivation of the first activated outputs.

Time resolved ellipsometry is applied to investigate heat diffusion processes occurring in polymer coated silicon under pulsed excitation. Experimental results, modelisation and analysis are presented.

In this paper, we have used an IR imaging system coupled with an IR detector to explore the periodically heated field in order to measure thermal diffusivity. Results on low diffusivity materials such as polymers are shown.

In this work a thick interface model is proposed in order to describe the photothermal signal perturbation introduced by grain interfaces. The validity of the model is discussed based upon photothermal reflectance microscopy results obtained on Fe sintered samples. A comparison with the thermal resistance model, which is valid only in the case of thin interfaces, is also presented.

The feasibility of transcranial high‐intensity focused‐ultrasound (HIFU) therapy within the brain relies on the ability to transmit ultrasound through the skull bone at relatively high ultrasound power. Absorption of ultrasound through the skull bone may cause important temperature rises, and is therefore an important parameter to control. Ultrasonic measurements have shown that the ultrasound beam undergoes a significant attenuation when propagating through the skull, with values on the order of 10 to 20 dB/cm/MHz. To predict temperature rise from such values, it is fundamental to weigh the relative role of absorption to the total ultrasonic attenuation (scattering + absorption + specular reflection). In this work, two types of numerical simulations and experiments are performed to investigate this relative role. Through‐transmission of 1 MHz ultrasound was performed numerically using a 3D Finite‐Difference Time‐Domain (FDTD) algorithm coupled to a 3D bone model obtained from high‐resolution synchrotron ...

Although optical waves do not exhibit the same ability to be manipulated as e.g. electromagnetic waves up to a few GHz or acoustic waves, for which field emitters‐detectors are available, various tools are nevertheless available in the optical domain which open the path to tricks which can be used in the context of sound‐light detection. In the purely optical domain, one knows the impact of deformable mirrors led to adaptive optics which is now coupled to OCT for retinal examination. Real time holography leads to complex wavefront synthesis and are useful in acousto‐optics (AO) to monitor very complex speckle field distributions. Phase conjugation which is in certain conditions equivalent to time reversal, starts to be used for wavefront retrieval after propagation in turbid media, one can think to use it for AO signal monitoring; moreover matrices of spatial light modulators allow to control light not only spatially but also in the frequency domain and open the field to new astonishing experiments. We wi...

This presentation will discuss the opportunity to use photoacoustics to guide high‐intensity focused ultrasound (HIFU) in biological tissue. The photoacoustic effect consists in the emission of sound by an illuminated optically absorbing region, based on the thermoelastic expansion following the absorption of a light pulse. In the near‐infrared range (700 nm to 900 nm), the absorption of light in biological tissue is relatively low, and multiply scattered photons can travel as deep as a few centimetres in tissue. Photoacoustic waves can therefore be generated deep in tissue, and have recently been used in vivo to perform passive acoustical imaging of optical absorbing features, such as blood vessels. We recently demonstrated on tissue‐mimicking phantoms that photoacoustics could be coupled to time‐reversal to automatically focus ultrasound towards an optical absorber [Bossy et al., APL 89(18), 2006]. We propose to further develop this approach to automatically guide HIFU therapy beams towards a targeted r...

We recently demonstrated experimentally that optically absorbing regions embedded at centimetric depths in an optically diffusive medium can be used, through the photoacoustic effect, as ultrasound sources for time‐reversal techniques [Bossy et al., APL 89(18), 2006]. If the optically absorbing region is spatially localized, the emission of the time‐reversed photoacoustic waves provides a method to automatically focus ultrasound towards the absorbing region. In biological tissue, this approach has the potential to automatically guide high‐intensity focused ultrasound (HIFU) beams towards a targeted region labelled with an optically absorbing contrast agent. However, such an approach is conceivable only if the HIFU beam is guided towards the sole targeted region, and not towards other potentially strong endogenous optical absorbers (such as blood vessels). In this work, we present a method to selectively focus time‐reversed photoacoustic waves towards an exogenous wavelength‐dependent optical contrast agent. Experiments were performed in vitro on tissue‐mimicking phantoms, with nano‐particles as contrast agents. A tunable nanosecond pulsed laser was used with different optical wavelengths to generate photoacoustic waves. A multi‐channel time‐reversal ultrasound system was used to emit ultrasound signals derived from time‐reversed photoacoustic signals obtained with different optical wavelengths.

We recently demonstrated experimentally the possibility to optically detect transient perturbations generated by the acoustic radiation force, applied several centimetres deep in a tissue‐mimicking phantom [Bossy et al., APL 90(17), 2007]. We proposed a detection scheme based on the transient decorrelation (millisecond time scale) of optical speckle patterns formed by coherent laser light that propagates through the phantom during the application of the radiation force. We demonstrated that this approach allows to detect optical contrasts embedded several centimetres deep in the phantom, based on the time‐evolution of the correlation coefficient during the transient motion of the medium. In the present work, we demonstrate that this approach also allows the detection of shear mechanical contrast. Moreover, the shape of the observed decorrelation curve provides a way to discriminate between an optical contrast and a shear mechanical contrast. We are now currently investigating the feasibility of detecting with spatial resolution the propagation of a shear wave, based on its effect on localized acousto‐optic interaction.

International audience; Acousto-optic imaging of thick biological tissues can be obtained in real-time with an adaptive-wavefront holographic setup, where the holographic media is a self-developping photorefractive crystal. As a consequence, the interference signal resulting from the acousto-optic effect can be easily collected with a high etendue and fast single photodetector. We present a statistical model of the field propagating through the scattering media and show why the various acoustic frequency components contained in the speckle output pattern are uncorrelated. We then give a detailed description of the signal measured through the photorefractive effect, in order to explain the quadratic pressure response observed for the two commonly used configurations setup e.g an amplitude or a phase modulation of the ultrasound

International audience; We present a new and simple method to obtain ultrasound modulated optical tomography images in thick biological tissues with the use of a photorefractive crystal. The technique offers the advantage of spatially adapting the output speckle wavefront by analysing the signal diffracted by the interference pattern between this output field and a reference beam, recorded inside the photorefractive crystal. Averaging out due to random phases of the speckle grains vanishes, and we can use a fast single photodetector to measure the ultrasound modulated optical contrast. This technique offers a promising way to make direct measurements within the decorrelation time scale of living tissues

International audience; We describe an instrument for measuring the magnitude of birefringence of tomographic images and the principal directions of axes that uses thermal-light polarization-sensitive optical coherence tomography. The instrument permits full-field measurements with an axial resolution of 1.5 μm and a transverse resolution limited by diffraction. We obtained a sensitivity of 84 dB, limited by shot noise, when we integrated the signal for 1 s. We verified the validity of the measurement by measuring the birefringence of a variable phase shifter. We present typical results obtained with optical samples.

Using a CCD camera and a multichannel lock-in scheme, the authors have enhanced the capabilities of photoreflectance microscopy to obtain a 2D image without scanning the sample, thus dramatically reducing the acquisition time. The photoreflectance images presented show Joule and Peltier heating of a polycrystalline Si 1 kΩ resistor across which a 30 mA peak to peak sinusoidal current is forced.

Temperature maps of laser diode facets obtained by photothermal reflectance microscopy are presented. Biased double heterojunction InGaAsP lasers were investigated. The temperature images reveal the influence of laser mode on the spatial distribution of the heat dissipation in the device. Moreover, a study of the modulated reflectance as a function of the injection current is achieved.

We have developed a new technique, photothermal displacement spectroscopy, for studying the optical and thermal properties of surfaces. Photothermal displacement spectroscopy is based on optical detection of the thermal expansion of a sample as it is heated by absorption of electromagnetic radiation. Details of the experimental configuration are shown. An optical absorption spectrum is generated as an intensity modulated, tunable light beam (pump beam) is focussed onto the sample, and, depending on the optical cross section, some fraction of the radiation is absorbed. As the excited electrons decay nonradiatively, the sample is heated. The illuminated surface is then displaced as the sample expands. A probe beam reflected from the surface is deflected by the slope of the surface displacement. This deflection is measured by a position sensitive photodiode whose output is then amplified by a phase sensitive lock-in amplifier referenced to the pump beam modulation. Thermal information can be obtained by measuring the shape and phase of the photothermal displacement relative to the illumination as a function of the modulation frequency.

We present a sensitive (5ppb for ethylene, 10−7 cm−1) and simple photothermal scheme for the detection of trace gases and measuring weak absorption in gas‐phase samples. We also demonstrate the feasibility of this scheme for performing in situ measurements in the absence of sample cells or containers, thus eliminating the drawbacks of sampling and sampling techniques. Factors limiting our detectivity are discussed, and a comparison to the thermal lens effect is made.

International audience; The measurement of optical contrasts within thick biological tissues can be performed with the hybrid technique of acousto-optic imaging, but it has been shown that an acquisition rate in the 1−10kHz range is required for a good efficiency. This comes from the interferometric nature of the signal, blurred by speckle decorrelation in a time c, due to a decrease of the speckle pattern contrast at the exit of the sample. An holographic setup that associates a fast and large area single photodetector and a photorefractive crystal, can measure in real-time the acousto-optic signal: this is the so-called self-adaptive wavefront holography technique. Nevertheless, it is essential to size the photorefractive response time (PR) of the crystal with c in order to optimize the signal-to-noise ratio of the measurement. This time mainly depends on the overall light intensity within the crystal. We have developed an original in situ method to determine PR with the combination of acoustic pulses and a frequency de-tuning of the reference beam. We can measure precisely this time but also monitor it according to a theoretical model that we have previously described. We are able to adapt the response time of the setup to the decorrelation time of the medium under study