The Use of a Toroidal Mirror as a Focusing Element for a Stigmatic Grazing Incidence Spectrometer

A toroidal mirror can be used in conjunction with a spherical grating grazing incidence spectrometer for producing a stigmatic system. The aberrations of the configuration are considered; they set the limits of the performance of the system. It is, however, possible by choosing suitable optical parameters to have a system that produces stigmatic images of small sources at various wavelengths in the region of grazing incidence from 10 to 300 +. The aberrations are quite small and comparison with other devices used to get spatial and spectral resolution is good. The proposed configuration is considerably better at forming stigmatic images than the corresponding one that uses a toroidal grating.