4. Optical assemblies with concave grating

4.1 Concave grating polychromator

Although a large number of optical assemblies have been described using standard gratings, only a small number are actually in use. Polychromators using concave gratings are based on the Paschen-Runge configuration. Concave gratings are used not only for diffraction, but also for collimation. The Paschen-Runge setup uses the Rowland circle, where a spherical concave grating of radius R is located on the perimeter of a circle of diameter equal to R (figure 8 ), with the grating lines perpendicular to the plane of the circle. The advantage of such an arrangement is that, if the entrance slit is located...