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Température effective d'un système hors équilibre : fluctuations thermiques d'un microlevier soumis à un flux de chaleur

Abstract : Thanks to a home made quadrature phase differential interferometer, we measure the thermal fluctuations ofa cantilever. It is then possible to infer various mechanical properties such as eigenfrequencies, stiffness,quality factor, etc. In such system, the maximal precision on the measure is limited by the shotnoise of thephotodiodes. To increase the signal-noise ratio we raise the light intensity of the laser, lowering thebackground noise. Doing so, the cantilever eigen frequencies shifts to lower values. A fisrt part of this thesiswork has for objective the understanding of this phenomenon. Thus, we associate this frequency shift with aheating of the cantilever by the laser. We develop a model linking this effect to the temperature at the freeend of the cantilever assuming a linear temperature profile.A second part of this thesis leads us to estimate the effective temperature of a cantilever using thefluctuation-dissipation theorem. We show that the fluctuations of our out of equilibrium system are lower thanthe fluctuations expected at equilibrium.In the last part, we estimate the temperature profiles on cantilevers by varying their geometry, absorptioncoefficient and laser position.
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Submitted on : Monday, November 30, 2015 - 4:15:06 PM
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  • HAL Id : tel-01235762, version 1

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Mickaël Geitner. Température effective d'un système hors équilibre : fluctuations thermiques d'un microlevier soumis à un flux de chaleur. Optique [physics.optics]. Ecole normale supérieure de lyon - ENS LYON, 2015. Français. ⟨NNT : 2015ENSL1026⟩. ⟨tel-01235762⟩

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