IMAGE EVALUATION OF THE HIGH-RESOLUTION VUV SPECTROMETER AT SURF-II BY RAY-TRACING

A high resolution VUV spectroscopic facility has been in use for sever al years at SURF II, the Synchrotron Ultraviolet Radiation Facility at the National Institute of Standards and Technology in Gaithersburg, M aryland. At this facility, a combination of three cylindrical mirrors is utilized to focus the light originating in the storage ring onto th e horizontal entrance slit of the spectrometer. The spectrometer uses a 6.65 m concave grating having a groove density of 4800 lines/mm in t he off-plane Eagle mounting. In preparation for the installation of an array detector in the exit image plane, a ray tracing program has bee n formulated and spot diagrams have been constructed by plotting the c oordinates of the points of intersection of the diffracted rays with t he image plane, which is tangent to the Rowland circle. In creating th e spot diagrams, we have considered both parallel and tilted configura tions of the entrance slit with respect to the grating grooves. It is shown that the line widths of the spectral images can be reduced when the entrance slit is properly tilted. Finally, we have estimated the s pectral widths of the images when they are recorded on an array detect or placed tangent to the Rowland circle. We conclude that an image spe ctral width of 0.41 pm to 0.88 pm in first order can be achieved over the wavelength region of 40 nm to 120 nm.