Improving the spectral resolution of soft x-ray flat-field spectrometer with multi-area gratings

摘要

The ideal focal curve for the soft x-ray flat-field spectrometer is a straight line, but the real one is not, thus the inconformity of aberrations between different wavelengths in the working waveband is inevitable. In order to further reduce aberrations and improve spectral resolutions, multi-area gratings (divided perpendicular the direction of grating grooves) are devised. Firstly, the grating is divided into three areas, and the spectral aberrations for these areas are analyzed by means of ray tracing. Then, diffraction efficiencies for the areas with worse aberrations should be reduced to lower the proportion regional aberrations contributing to the overall aberration, therefore better spectral image could be obtained and the spectral resolution would be improved. Theoretical analysis demonstrates that: using multi-area grating, the spectral resolutions at wavelength of 0.8 and 1.1 nm are increased from 123 and 333 to 401 and 671, respectively. At the same time, the spectral resolutions at other wavelengths are not reduced.