| CPC G01N 21/4133 (2013.01) [G01N 21/45 (2013.01); G01N 2021/451 (2013.01)] | 18 Claims |

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1. A sensor, including:
a planar entry guide comprising a first exit face and a planar transmission exit guide comprising a second entry face,
a Fabry-Pérot cavity configured to accommodate a fluid, and delimited by the first exit face of the planar entry guide and by the second entry face of the planar transmission exit guide,
a planar reflection exit guide optically coupled to the planar entry guide by the Fabry-Pérot cavity, having an optical axis at the first face forming an acute opening angle with an optical axis at the first face of the planar entry guide,
the Fabry-Pérot cavity being arranged so that a normal to the first face constitutes a bisector of the opening angle.
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