You are here

High-Accuracy Angle Generator for Precision Measurements


More accurate angle generators would allow NIST and other metrology laboratories to lower uncertainty in high-precision angle measurements. These generators would provide a needed tool for NIST and other world leading metrology laboratories to understand how surface flatness affects the measurement of angle using autocollimators, which is the de-facto tool for high accuracy angle measurements at NIST. These effects are the limiting uncertainty component in angle measurements that support R&D in critical technology intensive sectors.


X-ray studies at synchrotron light sources of the atomic structure of materials, biological molecules, etc. are currently limited by the quality of the x-ray spot focused onto the specimen. The quality of the focused spot is determined by the form accuracy of the mirrors used to focus the beam, typically a pair of elliptically-shaped mirrors used at grazing incidence. Improvements to the form accuracy of these mirrors are limited by the current abilities of metrology techniques. Specifically, improvements to the measurement of the local surface slope are needed. Metrologists at these synchrotron light sources are now using an autocollimator-based scanning technique to measure the surface profile for large (up to 1.5 m length), curved mirrors [1,2]. Effects of the curvature of the surface under test on the accuracy of the autocollimator used to measure the local surface slope need to be characterized to achieve the required tolerances of the mirrors.


Next-generation photonic devices incorporate various components whose geometry must be well characterized. NIST is currently measuring the angular attributes of these artifacts for industrial customers using autocollimators. Uncertainty components due to non-flat surface for these measurements are not well understood and published reports in this area are not exhaustive [3].


The goal is to develop precision angle generators that have accuracies that are better than what is currently commercially available. It is desired that the angle generator be able to accommodate mirrors with clear apertures between 2 mm and 35 mm that are up to 300 mm ´ 50 mm  ´ 50 mm in size (i.e., approximate size of curved mirrors used at synchrotron light sources).

Phase I expected results:
Experimentally prove the feasibility of fabricating an angle generator with an expanded uncertainty (k=2) of less than 0.01 arc-seconds over an angular range of 2.5 degrees.


Phase II expected results:
Provide a prototype automated precision angle generator with a rigorously documented uncertainty budget demonstrating that the target uncertainty requirements, an expanded uncertainty (k=2) of less than 0.01 arc-seconds over an angular range of 2.5 degrees, are met.


NIST will be available for consultation and collaboration as necessary.


[1] Geckeler, R.D., Just, A., Krause M. and Yashchuk, V.V. “Autocollimators for deflectometry: Current status and future progress”, Nucl. Instrum. Methods Phys. Res. A 616 (2010) 140–146.

[2] Yandayan, T., Geckeler, R.D. and Siewert, F. “Pushing the limits – latest developments in angle metrology for the inspection of ultra-precise synchrotron optics”, Proc. SPIE 9206, Advances in Metrology for X-Ray and EUV Optics V, 92060F (2014).

[3] Kruger, O.A. “Methods for determining the effect of flatness deviations, eccentricity and pyramidal errors on angle measurements”, Metrologia 37 (2000) 101–105.

US Flag An Official Website of the United States Government