Broadband reflective spectrometer for high-resolution spectral characterization of radiation sources

The development of compact radiation sources for extreme ultraviolet (EUV) radiation has enabled a multitude of lab-size applications, especially in the field of metrology, that were previously only possible at synchrotron facilities. Plasma-based and high-harmonic generation (HHG) sources are widely used and well characterized at their application specific wavelength ranges in the EUV regime. The spectrum of the emitted radiation from these sources extends to a broader wavelength range, even into the visible and infrared bands and their full spectral composition is not sufficiently characterized. Therefore, a broadband spectral characterization of the source emission is of utmost importance for the investigation of photon-induced processes and metrology. In this study, the authors present a unique setup and corresponding measurement results for the high-resolution broadband spectral characterization of radiation sources covering the extensive wavelength range from 5nm to 1μm. For the vacuum wavelength range (5nm to 200nm) the setup employs a combination of three flat-field diffraction gratings with varying line density as dispersive elements. Higher diffraction orders are filtered out by a selection of thin film filters. The wavelength range above 200nm is measured with two Czerny-Turner spectrometer modules. The resulting spectra are combined to obtain the full spectrum without any contributions from higher diffraction orders. Here, the overall design, wavelength calibration, and the relative and absolute intensity calibration of the measured spectra are presented.