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Résonateurs à ondes acoustiques de volume piégées à très basses température : Applications à l'optomécanique

Abstract : For a few years, the Time and Frequency department in FEMTO-ST Insitute has been leading research about the behavior of Bulk Acoustic Wave (BAW) trapped in quartz crystal at cryogenic temperatures (near 4K).The measured quality factor are around a few billions at few tens of MHz for such temperatures. Acoustical quartz cavities are therefore good candidates for ultrastable cryogenic frequency sources. The work presented here is in the natural continuation of the research cited above. They aim at strenghtening the interest for quartz crystal, but also to consider alternative solutions with non-piezoelectric material with very-low acoustical losses, for which optical excitation is an option. The following work can be summed up in three main parts:- The first part is about the determination of a quartz crystal cut for which a turnover point exists in the frequency-temperature curve in the cryogenic region. Indeed, it is not enough to barely control the temperature in an ultrastable frequency source. Such a turnover point needs to be the operation point for thermal regulation. Searching a compensated cut arose the need for a preliminary measurements campaign of thermal coefficients of elastics coefficients of the material, which were unknown at low temperature. It was then possible, based on these coefficients, to calculate and even realize a cut fulfilling the required condition.- The second part had the objective to demonstrate conceptually that using a quartz acoustical cavity as an optical cavity was feasible. In its basic scheme, a BAW quartz resonator is plano-convex (to ensure the trapping of the acoustic wave) and has electrodes (metal-made to ensure electrical excitation) deposited on each face. It has been demonstrated, both theoretically and experimentally, that such a geometry works fine as an optical cavity, with its corresponding advantages and limitations. This scheme is used for the optomechanical coupling discussed in the third part and constitutes the very base for more efficient optomechanical devices.- The third part is dedicated to the evaluation of how efficient will such devices be while functioning at cryogenic temperature. A theoretical quantification of the optomechanical coupling that these cavities might reach is also presented.
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Submitted on : Friday, December 13, 2019 - 2:15:07 PM
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  • HAL Id : tel-02409399, version 1

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Jérémy Bon. Résonateurs à ondes acoustiques de volume piégées à très basses température : Applications à l'optomécanique. Optique / photonique. Université Bourgogne Franche-Comté, 2018. Français. ⟨NNT : 2018UBFCD059⟩. ⟨tel-02409399⟩

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