The wavelength reconstruction from toroidal spectrometer image data

Abstract

We are reporting spectroscopy studies of Nitrogen filled capillary discharge. The identification procedure of spectra was carried out with the use of an extreme ultraviolet grazing incidence spectrometer with toroidal grating. The source of radiation and the object under study is a pinching alumina capillary discharge in Nitrogen, where stimulated emission in the 13.4 nm wavelength region is expected. To simplify the alignment of the spectrometer during the experiment the off Rowland circle registration scheme is used. In this scheme, spectra are recorded in a single plane and thus exact focusing of the input slit takes place only for one single wavelength, which corresponds to the intersection of the plane of registration with the Rowland circle. Appropriate image processing must be applied to reconstruct the spectra profile and to calibrate wavelength positions. The cooled extreme ultraviolet sensitive CCD camera was used in the role of planar detector. It has a 512×512 elements matrix with 24 µm square pixels. The 16-bit dynamic range together with very low-noise provide a good data source for image post-processing. The experimental impossibility to record simultaneously zeroth order maximum and the first diffraction order spectrum was a crucial problem in the presented process. The presented methodology can be applied to any experiment using toroidal grating spectrometer.