Recent advances in spatial angle autocollimator calibration at PTB

In this contribution, we present our latest improvements of the Spatial Angle Autocollimator Calibrator (SAAC) at the Physikalisch-Technische Bundesanstalt (PTB). The SAAC is capable of traceable spatial angle calibration of autocollimators at a variable optical path length. Autocollimators are used for example in profilometers for the precision form measurement of optical surfaces. An essential part of the SAAC is the mathematical modelling of the spatial orientation of all components relative to each other. By choosing an appropriate reference system and a numerical description of spatial rotations with quaternions it is possible to increase the flexibility with respect to the geometrical arrangement of the components and the choice of sampling points. Furthermore a reduction in error propagation is achieved. The centrepiece of the data analysis is a multi-stage optimisation algorithm based on the Nelder-Mead method. We will present the results of extensive Monte-Carlo simulations and compare them with long term measurements under typical environmental conditions.