In 2019, the Institut für angewandte Photonik (IAP) e. V. in cooperation with Nano Optics Berlin (NOB) GmbH and SIOS Meßtechnik GmbH has made an important progress in the technology for precision soft X-ray optics – the development of three-dimensional (3-D) reflection zone plates (RZPs) with diffractive compensation of slope errors. 2-D mapping of spherical and toroidal grating substrates was used for the metrology of their individual profile. Based on these data, the inscribed grating structure, which corrects the slope error distribution, was computed. The correction algorithm has been implemented as a Python script, and first pilot samples of slope error compensated RZPs are in fabrication process. The 3-D device can replace two or three components in an optical scheme and, therefore, reduce absorption losses by several orders of magnitude. Beyond, the fabrication of customized 3-D Fresnel structures on curved substrates promises considerable improvements for efficiency, resolution and energy range in wavelength dispersive applications. As an example, we present simulations for a compact instrument within (150 – 250) eV. Further development of this approach toward commercial availability will enable the design and construction of compact soft Xray monochromators and spectrometers with unique parameters.
The sensitivity of soft X-ray instrumentation for use in spectroscopy and monochromatization in the Hettrick-Underwood (HU) configuration can be significantly enhanced by replacing the common one-dimensional (1-D) variable line space grating by a two-dimensional (2-D), point-focusing reflection zone plate (RZP). To demonstrate the gain in the performance, we present examples of a flat-field spectrometer for the TiO2 fluorescence between about 390 eV and 530 eV and a femtosecond (fs) monochromator for an energy as low as 38.5 eV. In this context, the application to laser-based high harmonic generation (HHG) sources is discussed.