Mechanical alignment of optical system: CMMs forces and damages on optical elements

Traditional alignment techniques for optical systems are usually based on iterative procedures where each optical element is positioned and aligned with push-pull systems and the feedback is provided by the images acquired on the focal planes. The long-term stability of those optomechanical mounts can be critical and, In order to overcome this limitation a new mounting has been proposed together with a new alignment strategy based on the direct mechanical measurement of the optical surfaces. The contact between the probe and the surfaces of the optics can be a critical point and lead to different alignment strategies. In this paper, the forces applied by different Coordinate Measuring Machines (CMMs) will be presented together with a derived theoretical model. Moreover, the results of the damage tests performed on different optical elements will be shown and some general prediction rule will be presented.