An optical cavity, includes: a set of elliptical mirrors, which are intended to receive light radiation emitted by a light source, the light radiation leaving the elliptical mirrors being intended to he received by a detector; a first common focal point and a second common focal point, which are shared by the set of the elliptical mirrors, the light source being intended to he arranged at the first common focal point, the detector being intended to be arranged at the second common focal point; a contour, comprising a part formed by the set of the elliptical mirrors which are arranged consecutively.