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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; 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).