X-Ray Optics Metrology Laboratory

Long Trace Profiler

The long trace profiler (LTP) measures slope and curvature of mirror surfaces along one dimension using a zero-path difference interferometer. The APS LTP can measure optical surfaces up to 2 meters in length, probing the spatial frequency range of 0.25-0.0005 cycle/mm.

Surfaces of any shape can be measured, so as long as the surface slope change is within the +/-5 milliradian acceptance angle of the LTP optical system, with a sensitivity of 0.1 miroradian (0.02 arsec.) in slope and 0.5 nm in height. Improvement of the local environment of the LTP enabled us to reach a repeatability of 0.5 microradian.


Example of the LTP output: surface slope error (red curve) measured on an 1000-mm- -long mirror, the corresponding height profile (blue curve) is obtained by intergrading the surface slope error profile.

Recent Enhancement of the LTP Capabilities

The standard LTP setup can only measure a mirror surface that is facing up. However, in some cases mirrors are designed to deflect x-ray beams downwards or sideways, and so characterization of mirrors and mirror-bender assemblies in their intended orientation is desirable. In order to do so, a special scanning arm has been designed and implemented in the APS LTP. This scanning system (see the photograph below) is composed of a double pentaprism system and is modular. The first pentaprism is used to deflect the beam by a 90-deg. angle in order to measure mirrors deflecting sideways (this is also useful in eliminating deflection due to gravity). The second pentaprism bends the probe beams by a additional 90-deg. angle in order to measure mirrors in the downwards deflecting position. The position of the probe beams can easily be adjusted to measure any location on the test surface.


Photograph of the APS LTP with a mirror-bender system under evaluation and calibration. The mirror surface is facing downward, and a special scanning arm was designed and implemented in order to measure the mirror surface.

 

Conatct: Lahsen Assoufid, assoufid@aps.anl.gov