Optical focusing and collection system, intended to focus, on a sample to be analysed, a so-called primary light beam emitted by an optical emitter, and to collect a so-called secondary light beam emitted by the sample in response to the primary light beam and to transmit it to a photodetection system, this optical system including a plurality of optical parts (10, 20, 30) each centred on one and the same principal optical axis (Δ), including: ∘ a first forming optical part, adapted to receive the primary light beam on an entry surface, and to supply the primary light beam made annular about the principal optical axis (Δ) by an exit surface; ∘ a second focusing and collection optical part, including: • a conical so-called top central reflective surface, formed by a central zone (21.2) surrounded by a peripheral zone (21.1) and adapted to reflect, by the peripheral zone (21.1), the annular primary light beam coming from the exit surface of the first optical part, and to reflect, by the central zone (21.2), the incident secondary light beam coming from a so-called bottom central reflective surface; • the conical bottom central reflective surface, adapted to reflect and focus on the sample the incident primary light beam coming from the top central reflective surface; and to collect and reflect the secondary light beam emitted by the sample; • at least two frustoconical peripheral reflective surfaces (22; 23), optically coupling the top and bottom central reflective surfaces; ∘ a third return optical part, including a reflective surface: • located between the exit surface of the first optical part and the top central reflective surface of the second optical part, on the principal optical axis (Δ) and having transverse dimensions smaller than those of the annular primary light beam supplied by the exit surface, and • adapted to reflect, in the direction of the photodetection system, the secondary light beam coming from the central zone (21.2) of the top central reflective surface. ∘ a first forming optical part, adapted to receive the primary light beam on an entry surface, and to supply the primary light beam made annular about the principal optical axis (Δ) by an exit surface; ∘ a second focusing and collection optical part, including: • a conical so-called top central reflective surface, formed by a central zone (21.2) surrounded by a peripheral zone (21.1) and adapted to reflect, by the peripheral zone (21.1), the annular primary light beam coming from the exit surface of the first optical part, and to reflect, by the central zone (21.2), the incident secondary light beam coming from a so-called bottom central reflective surface; • the conical bottom central reflective surface, adapted to reflect and focus on the sample the incident primary light beam coming from the top central reflective surface; and to collect and reflect the secondary light beam emitted by the sample; • at least two frustoconical peripheral reflective surfaces (22; 23), optically coupling the top and bottom central reflective surfaces; • a conical so-called top central reflective surface, formed by a central zone (21.2) surrounded by a peripheral zone (21.1) and adapted to reflect, by the peripheral zone (21.1), the annular primary light beam coming from the exit surface of the first optical part, and to reflect, by the central zone (21.2), the incident secondary light beam coming from a so-called bottom central reflective surface; • the conical bottom central reflective surface, adapted to reflect and focus on the sample the incident primary light beam coming from the top central reflective surface; and to collect and reflect the secondary light beam emitted by the sample; • at least two frustoconical peripheral reflective surfaces (22; 23), optically coupling the top and bottom central reflective surfaces; ∘ a third return optical part, including a reflective surface: • located between the exit surface of the first optical part and the top central reflective surface of the second optical part, on the principal optical axis (Δ) and having transverse dimensions smaller than those of the annular primary light beam supplied by the exit surface, and • adapted to reflect, in the direction of the photodetection system, the secondary light beam coming from the central zone (21.2) of the top central reflective surface. • located between the exit surface of the first optical part and the top central reflective surface of the second optical part, on the principal optical axis (Δ) and having transverse dimensions smaller than those of the annular primary light beam supplied by the exit surface, and • adapted to reflect, in the direction of the photodetection system, the secondary light beam coming from the central zone (21.2) of the top central reflective surface.