Abstract: The device comprises a target member (4) and a support (1) for supporting the target member. The support includes a receptacle head (12) for the target member, including a housing (15) open to the outside via an outwardly flared frustoconical seat (16). The target member includes a flange (42) having a spherical annular lateral surface adapted to bear tangentially against the seat (16), and a plate (45) upstanding perpendicularly on the flange in an equatorial plane an imaginary sphere (44) of which the lateral surface of the spherical annular flange is part. The plate has two parallel plane retroreflecting faces and a hole (46) passing completely through it and centered on an axis perpendicular to the faces of the plate and passing through the center of the spherical surface, and the hole is open at both ends via a bevel (461).