RISE: robust iterative surface extension for sub-nanometer X-ray mirror fabrication.

Area of Science:

• Optics and Photonics
• Materials Science
• Metrology

Background:

• Precision optics, like X-ray mirrors, are vital for advanced facilities such as synchrotrons and free electron lasers.
• Achieving sub-nanometer surface accuracy (RMS) in the Clear Aperture (CA) is essential for diffraction-limited X-ray imaging.
• Current surface extension methods struggle with boundary errors and noise, hindering sub-nanometer polishing.

Purpose of the Study:

• To develop a novel surface extension method for X-ray mirrors that overcomes limitations of existing techniques.
• To enable the fabrication of X-ray optics with sub-nanometer surface precision.
• To improve the accuracy of dwell time calculation in polishing processes.

Main Methods:

• Proposed a Robust Iterative Surface Extension (RISE) method utilizing a data fitting strategy.
• Modeled figure errors in the Clear Aperture (CA) using orthogonal polynomials, fitting only correctable errors.
• Implemented iterative refinement of dwell time, incorporating boundary conditions to compensate for extension and deconvolution errors.

Main Results:

• The RISE method significantly reduces figure error residuals in the CA.
• The total dwell time increase was negligible.
• Experimental verification showed figure errors improving from over 190 nm RMS to below 0.71 nm RMS for 10 mm x 80 mm CAs.

Conclusions:

• RISE is the first data fitting-based surface extension method for precision optics.
• RISE is the first method to optimize dwell time through iterative extension.
• The method effectively enables sub-nanometer level X-ray mirror fabrication, meeting stringent precision requirements.