ILLUMINATION OPTICAL DEVICE COMPRISING A COLLIMATOR HAVING LOW INTRINSIC NOISE

The illumination optical device comprises a collimator, a light source, and an aperture. The collimator comprises a primary mirror, a secondary mirror, a tertiary mirror and a quaternary mirror mutually tilted so as to form a collimator optical path extending between the light source and the aperture and formed, in succession, by the light source, the quaternary mirror, the tertiary mirror, the secondary mirror, the primary mirror and the aperture. The light source is configured to emit light rays, along respective directions, which form a main beam propagating along directions intercepting the quaternary mirror so as to follow the collimator optical path; and a secondary beam propagating along directions not intercepting the quaternary mirror. The illumination optical device is characterised in that the collimator comprises a shielding structure configured to prevent illumination of the aperture by the secondary light beam.