Abstract

In a previous paper, the University of Arizona (UA) has developed a measurement technique called: Software Configurable Optical Test System (SCOTS) based on the principle of reflection deflectometry. In this paper, we present results of this very efficient optical metrology method applied to the metrology of X-ray mirrors. We used this technique to measure surface slope errors with precision and accuracy better than 100 nrad (rms) and ~200 nrad (rms), respectively, with a lateral resolution of few mm or less. We present results of the calibration of the metrology systems, discuss their accuracy and address the precision in measuring a spherical mirror.

Highlights

  • Focusing light to nanometer length scales and preserving the high brightness made available by third and fourth generation synchrotron/FEL sources requires significant advances in the quality of reflective EUV, soft X-ray and X-ray optics and in the metrology used to optimize their fabrication

  • The form of these elements can be corrected at the nanometer level by computer controlled polishing or ion beam figuring but the accuracy of absolute form metrology limits the possibilities of the manufacture of modern optical elements

  • We show how the Software Configurable Optical Test System (SCOTS) can be used to perform high accuracy optical metrology for X-ray mirrors

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Summary

Introduction

Focusing light to nanometer length scales and preserving the high brightness made available by third and fourth generation synchrotron/FEL sources requires significant advances in the quality of reflective EUV, soft X-ray and X-ray optics and in the metrology used to optimize their fabrication. The transport and monochromatization of X-ray/EUV light from a high brilliant source to the sample without significant loss of brilliance and coherence is a challenging task in X-ray optics and requires optical elements of very high accuracy [1,2,3,4] These are wavefront preserving plan or highly focusing mirrors with lengths of up to 1 m characterized by residual slope errors in the range of 50 nrad rms and values of 0.3 nm rms or less for micro-roughness [5]. Today, manufacturing techniques allow for figuring arbitrary optical surfaces The form of these elements can be corrected at the nanometer level by computer controlled polishing or ion beam figuring but the accuracy of absolute form metrology limits the possibilities of the manufacture of modern optical elements.

Mathematical description and principle of SCOTS
Synchronous detection
Transverse ray aberration model
Tradeoff between spatial resolution and slope sensitivity
SCOTS test of a long radius spherical mirror
Calibration of the test with a plano mirror
Sensitivity to camera mapping distortion
Effect from lens pupil aberration
Effect from lens imaging
Effect from the screen substrate shape errors
Effect from system geometry and alignment
Summary of test uncertainties
Findings
Conclusions

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