Related Experiment Video
Updated: Jun 8, 2026
10:39
Measurement of X-ray Beam Coherence along Multiple Directions Using 2-D Checkerboard Phase Grating
Published on: October 11, 2016
Surface finish requirements for soft x-ray mirrors.
Applied Optics
|October 2, 2010
Summary
For high-performance x-ray mirrors, surface roughness must be below 1 Å across a wide spatial frequency range. Standard metrology can be misleading; scanning-probe techniques are crucial for accurate surface characterization.
Area of Science:
- Materials Science
- Optics
- Metrology
Background:
- X-ray multilayer mirrors are critical for various applications requiring high reflectance.
- Surface finish directly impacts mirror performance, especially at normal incidence.
- Characterizing nanoscale surface features is essential for optimizing mirror fabrication.
Purpose of the Study:
- To correlate direct surface-finish metrology with soft x-ray reflectance measurements.
- To establish critical surface roughness parameters for high-reflectance x-ray mirrors.
- To evaluate the suitability of different metrology techniques for x-ray mirror characterization.
Main Methods:
- Comparison of scanning-probe metrology with optical and stylus profilometry.
- Analysis of surface-finish Fourier spectra of highly polished x-ray mirrors.
- Measurement of normal-incidence, soft x-ray reflectance.
Main Results:
- High reflectance requires root-mean-square (rms) surface roughness below ~1 Å.
- This roughness criterion applies to spatial frequencies from 1 to 100 µm⁻¹ (1 µm to 10 nm wavelengths).
- Surface-finish Fourier spectra of these mirrors follow an inverse power law.
Conclusions:
- Scanning-probe metrology is essential for characterizing the relevant spatial frequencies.
- Bandwidth-limited roughness measurements from lower-spatial-frequency instruments are uncorrelated with soft x-ray reflectance.
- Inaccurate metrology can lead to erroneous conclusions about x-ray mirror performance.
