Conical diffraction of the synchrotron beam to probe the efficiency and morphology of blazed gratings

TL;DR

This paper demonstrates how synchrotron-based conical diffraction measurements can simultaneously assess the efficiency and surface morphology of blazed gratings, providing a powerful nanometrology tool supported by numerical simulations and microscopy data.

Contribution

It introduces the use of synchrotron conical diffraction patterns as a novel method to evaluate both the groove profile and surface roughness of blazed gratings.

Findings

Diffraction patterns are sensitive to groove profile.

Diffuse scattering depends on surface roughness.

Numerical simulations support experimental observations.

Abstract

This study explores the use of synchrotron measurements as a nanometrology tool for blazed gratings. In grazing incidence geometry, one can measure both the conical diffraction and the diffuse scattering on the grating simultaneously in a single scattering pattern. The sensitivity of scattering patterns to the structure of the blazed gratings is evaluated. The diffraction component of the pattern is shown to be sensitive to the average groove profile of the gratings. Meanwhile, the diffuse scattering depends on the roughness morphology of the reflective surface of blazed gratings. These findings are supported by numerical simulations. The simulations were performed using several rigorous solvers for the Helmholtz equations, and with a perturbation theory. The analysis relies on synchrotron data, as well as data from atomic force microscopy and scanning electron microscopy. The aim of this article is to draw the attention of the optical community to the synchrotron measurements as a nanometrology tool for the modern optical elements.