Single-order operation of lamellar multilayer gratings in the soft x-ray spectral range

Petra Hegeman,Robert Van Der Meer,Igor Kozhevnikov,Fred Bijkerk,Boris Vratzov,Bert Bastiaens,Balachander Krishnan,Klaus Boller,Jurriaan Huskens,Christian Brons

doi:10.1063/1.4774297

Abstract

We demonstrate single-order operation of Lamellar Multilayer Gratings in the soft x-ray spectral range. The spectral resolution was found to be 3.8 times higher than from an unpatterned multilayer mirror, while there were no significant spectral sideband structures adjacent to the main Bragg peak. The measured spectral bandwidths and peak reflectivities were in good agreement with our theoretical calculations.

Highlights

In the soft x-ray (SXR) wavelength range, the reflectivity response of multilayer (ML) mirrors is basically narrowband due to the Bragg reflection process, i.e. such mirrors are wavelength selective
The spectral resolution of ML mirrors is fundamentally limited by the inherent absorption of all materials in this wavelength range
The penetration depth can be increased by removing part of the absorptive material from the ML mirrors by etching a grating into the multilayer structure, resulting in a so-called Lamellar Multilayer Grating (LMG, see Figure 1).[2,3,4,5,6]

Summary

Introduction

In the soft x-ray (SXR) wavelength range, the reflectivity response of multilayer (ML) mirrors is basically narrowband due to the Bragg reflection process, i.e. such mirrors are wavelength selective. In the approximation of a semi-infinite and strictly periodic ML stack, single-order operation improves the spectral resolution by a factor 1/ while the peak reflectivity is maintained in comparison to conventional ML mirrors.[5]

Results

Conclusion