Autocollimators for Deflectometry: Current Status and Future Progress

摘要

The proliferation of autocollimator-based surface profilometers at synchrotron metrology laboratories worldwide necessitates a detailed understanding of the parameters influencing their angular response. A comprehensive overview of the current status of autocollimator characterization and calibration at the Physikalisch-Technische Bundesanstalt (PTB) and its implications for their optimal application are provided, as well as information on future challenges and expected progress. Autocollimator-based deflectometric profilometers are in operation at the PTB, the Advanced Light Source (ALS), Lawrence Berkeley National Laboratory, USA, the BESSY II, Helmholtz-Zentrum Berlin fuer Materialien und Energie GmbH, Germany, and the Diamond Light Source Ltd (DLS), UK. A continuous topic of research at the PTB is to investigate the factors influencing the angular response of autocollimators and to provide the most accurate calibration of the instruments to aid users in their application and manufacturers in their improvements. At the PTB, the calibration of autocollimators is realized by a direct comparison of the devices with the primary angle reference standard. With highly stable autocollimators, calibrations with standard measurement uncertainties of u = 0.003 arcsec (15 nrad) have been achieved. The influence of a number of parameters on the angle measurement with autocollimators have been investigated in detail, such as the reflectivity of the surface under test (SUT), the diameter and shape of the aperture stop, its position both along the autocollimator's optical axis and perpendicular to it, as well as the optical path length of the autocollimator beam. Extensive information on these errors and their minimization will be presented.