Non-contact XUV metrology of Ru/B4C multilayer optics by means of Hartmann wavefront analysis

TL;DR

This paper demonstrates a non-contact XUV wavefront sensing technique using Hartmann sensors to inspect Ru/B4C multilayer optics with nanometer precision, crucial for nano-scale optical applications.

Contribution

It introduces the first experimental application of Hartmann wavefront analysis in the XUV range for multilayer optics surface characterization.

Findings

Detects wavefront aberrations in the nanometer range.

Effective non-contact method for large surface inspection.

Applicable to high-precision optical manufacturing.

Abstract

Short-wavelength imaging, spectroscopy, and lithography scale down the characteristic length-scale to nano meters. This poses tight constraints on the optics finishing tolerances, which is often difficult to characterize. Indeed, even a tiny surface defect degrades the reflectivity and spatial projection of such optics. In this study, we demonstrate experimentally that a Hartmann wavefront sensor for extreme ultraviolet (XUV) wavelengths is an effective non-contact analytical method for inspecting the surface of multilayer optics. The experiment was carried out in a tabletop laboratory using a high-order harmonic generation as an XUV source. The wavefront sensor was used to measure the wavefront errors after the reflection of the XUV beam on a spherical Ru/B4C multilayer mirror, scanning a large surface of approximately 40 mm in diameter. The results showed that the technique detects the aberrations in the nanometer range.