Studies in Optimal Configuration of the LTP

摘要

Brightness preservation requirements for ever brighter synchrotron radiation and free electron laser beamlines require surface slope tolerances of x-ray optics on the order of 0.2 (xrad, or better. Hence, the accuracy of dedicated surface slope metrology must be 0.1 urad, or even less. Achieving this level of measurement accuracy with the flagship instrument at synchrotron radiation metrology laboratories, the Long Trace Profiler (LTP), requires all significant sources of systematic, random, and instrumental drift errors to be identified, and reduced or eliminated. In this respect, the performance of certain components of the Advanced Light Source LTP-II design [Kirschman, et al., Proc. SPIE, 7077, 70770A-12 (2008)] is analyzed, considering the principal justification for inclusion of each component, possible systematic error due to the quality of its optical material, and drift effects due to generated heat, etc. We investigate the effects of replacement of the existing diode laser with a fiber-coupled laser light source, and demonstrate that reducing the number of components by using a single beam on the surface under test (SUT), rather than an original double beam maintains, or even improves the accuracy of measurement with our LTP. Based on the performance of the upgraded LTP, we trace the further steps for improving of the LTP optical system.