High resolution monochromator covering wide ultraviolet spectral ranges with a single grating

A new configuration for a wide ultraviolet range high resolution monochromator has been analyzed. It consists of a first off-axis paraboloidal mirror collimating the radiation beam from the source, followed by a couple of plane optical elements, a mirror and a grating, constituting the dispersive system, and by a second off-axis paraboloidal mirror focusing a selected portion of the dispersed radiation beam on a fixed exit slit. Since in the extreme ultraviolet region it is necessary to use the optical elements in grazing incidence to have a good reflectivity, the two paraboloidal mirrors can be used in the so-called sagittal focusing to minimize the slope error induced aberrations in the dispersive plane. The wavelength scan is simply realized by means of two independent rotations, of the plane mirror and of the grating, while the other elements are fixed. As this configuration is geometrically aberration free, it is possible to choose different working conditions, for example to maximize the monochromator transmission or the higher order rejection, without worsening its high resolution performance. Moreover the stability of the tolerances of the optical elements constituting the dispersive system is not so critical as happens in many other monochromators offering similar performances. As an example, the monochromator performances when applied to a synchrotron radiation source in the range 250-1250 eV (9.9-49.6 angstroms) are shown.