Use of null optics for monitoring the optical alignment of a beam director

The use of null optics is proposed as a new concept for monitoring the optical alignment of a beam director. Null optics consist of a primary mirror and an annular mirror just outside the aperture of the secondary mirror. The characteristics of the proposed null optics are investigated with the designed sample of a two-mirror system with an effective aperture of 275 mm. The results show that null optics yield four times the amplification with respect to the alignment errors of the secondary mirror; however, they have low residual aberration sensitivity to misalignment. Therefore null optics can be used successfully as the alignment monitoring apparatus of a beam director.