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International audience; La connaissance déjà acquise sur la dynamique de la liaison hydrogène dans l'eau liquide grâce au développement de laser délivrant des impulsions ultra-courtes dans l'infrarouge moyen nous permet de filmer la rotation de molécules HDO dans une solution D2O. L'expérience réalisée au laboratoire est basée sur la technique de spectroscopie pompe sonde résolue en polarisation. L'anisotropie mesurée permet de détecter en temps réel l'angle de déflexion du moment dipolaire de transition dont le point de départ est la direction du faisceau laser de pompe.

International audience; A pump-probe experiment is described to study femtosecond dynamics of hydrogen bonds in liquid water. The key element of the experimental setup is a laser source emitting 150 fs pulses in the 2.5-4.4 urn spectral region, at 10 nJ power level. The OH-stretching band is recorded for different excitation frequencies and different pump-probe delay times. Time-dependent solvatochromic shifts are observed and are interpreted with the help of statistical mechanics of nonlinear optical processes. Using these spectral data, the OH -O motions are "photographed" in real time. Cop. EDP Sciences.

International audience

International audience; We describe a highly sensitive and stable quantum-cascade laser-based attenuated total reflection (ATR) terahertz sensor for the detection of very low concentration solutions, using a dual-modulation differential approach and ATR geometry. This sensor offers a very high dynamic range and along-term stability of 40 dB, which extends the potential of terahertz radiation for the analysis of liquid and biological samples. The performance is illustrated by measurements on standard solutions of ions, sugars, and proteins, for concentrations down to 1 M.

International audience; Using attenuated total reflection (ATR) in the terahertz domain, we demonstrate non-invasive, non-staining real time measurements of cytoplasm leakage during permeabilization of live epithelial cells by saponin detergent and after electropermeabilization. The origin of the contrast observed between cells and culture medium is addressed by both experimental and theoretical approaches, and gives access to permeabilization dynamics of live cells in real time. We show that terahertz modalities are more sensitive than fluorescence microscopy which is the reference optical technique for electropermeabilization. We propose analytical models for the influx and efflux of non-permeant molecules through permeabilized cell membranes.

International audience; Understanding the relevant parameters of the formation of pores during permeabilization is very challenging for medical applications. Several components are involved: the arrival of the permeabilizing molecules to the membrane, the efficiency of formation of the pores and their specific dynamics, and the flux of molecules through the plasma membrane. Using attenuated total reflection in the terahertz domain, we studied the dynamics of Madine-Darby canine kidney cells after permeabilization by saponin molecules. We developed an analytical model taking into account saponin molecule diffusion, cell geometry, cytosol molecule diffusion, and pore dynamics. We also studied the effect of possible pore overlapping on the cell membrane, introducing a dimensionless quantity that is the ratio between overlapping and diffusive effects. Pores are found to be static within 1 h after their creation, hinting that the diffusion of the saponin molecules to the membrane is the limiting factor in our experiments.

The failure to accurately delineate breast tumor margins during breast conserving surgeries results in a 20% re-excision rate. Consequently, there is a clear need for an operating room device that can precisely define intraoperatively breast tumor margins in a simple, fast, and inexpensive manner. This manuscript reports investigations that were conducted towards the ability of terahertz radiations to recognize breast malignant lesions among freshly excised breast volumes. Preliminary works on terahertz far-field spectroscopy have highlighted the existence of a contrast between healthy fibrous tissues and breast tumors by about 8% in refractive index over a spectral window spanning from 300 GHz to 1 THz. The origin for contrast was explored. Results seem to indicate that the dynamics of quasi-free water molecules may be a key factor for demarcation. On these basis, different methods for tissue segmentation based on refractive index map were investigated. A cancer sensitivity of 80% was reported while preserving a specificity of 82%. Eventually, these pilot studies have guided the design of a BiCMOS-compatible near-field resonator-based imager operating at 560 GHz and sensitive to permittivity changes over breast tissue surface.; La faible précision avec laquelle sont délimitées les marges d'exérèse des adénocarcinomes mammaires se traduit par un recours régulier à un second acte chirurgical. Afin d'en limiter la fréquence, la communauté scientifique tente de définir les grands axes de conception d'un système intraopératif permettant la reconnaissance des lésions mammaires malines. Ce manuscrit de thèse rapporte les investigations menées sur la capacité des ondes térahertz à fournir un contraste entre tissus mammaires sains et malins. Les premiers travaux ont montré l'existence d'un contraste sur l'indice de réfraction entre 300 GHz et 1 THz, évalué en moyenne à 8%. Ce dît contraste semble prendre origine dans la dynamique des molécules d'eau intrinsèques aux cellules cancéreuses. Différentes techniques de segmentation d'image, basées sur l'indice de réfraction des zones tissulaires, ont permis de rapporter une sensibilité au cancer jusqu'à 80% tout en maintenant un taux de spécificité de l'ordre de 82%. L'ensemble de ces études a guidé la conception d'un imageur champ-proche opérant à 560 GHz, dont la réponse des différents senseurs est sensible à la permittivité en surface des tissus du sein.

International audience; Terahertz radiation offers new contrasts with biological systems, without markers or staining, at the molecular, cellular or tissue level. Thanks to technological advances, it is increasingly emerging as a solution of choice for directly probing the interaction with molecules and biological solutions. Applications range from dynamics of biological molecules to imaging of cancerous tissues, including ion, protein and membrane sensors.

International audience; The electromagnetic wavefront diffracted by an object carries information about the shape of the object from which the wave was emitted. Being able to record the phase and intensity of such a wave thus allows to reconstruct the object from the information carried by the wave, even if the object is no longer present. Among the reconstruction techniques, holography plays a big part. However the waves may experience a great variety of distortions on their way from the object to the measurement apparatus. Thus being able to shape the wavefront at will is key in holography. Micromirror light modulators are powerful tools for that matter and are well known for holographic applications. This paper explores the fundamental principles for digitally reconstructing a precise image of an object, but also for digitally correcting an imperfectly shaped wavefront, by exploiting the diffraction properties of light on a reflective surface. The methods presented here have been implemented as part of practical work for 2nd year students at the Ecole Polytechnique (last year of undergraduate program).