Design of a flexure-based alignment device for adjustable and stable mounting of optical components

Measurement systems such as systems based on interferometric combination of beams of light, require highly accurate alignment of optical components such as mirrors to achieve fringes. Moreover, the stability of such alignment mechanisms must be even higher. Alignment devices based on flexures provide accurate alignment with excellent resolution, without play or hysteresis. TNO TPD developed mechanisms for adjustment of mirrors in two degrees of freedom, meaning two rotations, and used these mechanisms in setups to achieve picometer stability. The paper describes the design process and the development of a set of alignment mechanisms. Theoretical and practical aspects are mentioned. First the design aspects for designing stable mounts are given, and then two mechanisms are described. The mechanisms consist of a monolithic adjustment mount for a mirror that is made by wire erosion in such a way that the mirror can rotate about two axes. Adjustment screws in combination with a lever and a gear provide easy and accurate adjustment of the rotation of the mirror. The combination of flexures result in a virtual point of rotation that is positioned on the centre of the mirror surface. In this case, the optical path length of the deflected light path will not change. Two degree of freedom rotation mechanisms have a generic design, so the design can be used in multiple instruments. The measurement systems show high stability of the components.