Rowland Circle Concave Gratings

Rowland circle gratings represent a specific type of imaging grating characterized by a configuration in which the entrance slit, the grating, and the detector must all lie on the diffraction circle—known as the Rowland circle. Although the slit image suffers from astigmatic elongation, the Rowland circle configuration enables coma-free imaging, thereby ensuring high spectral resolution.
Compared to other imaging gratings, the grating structure on the spherical surface of a Rowland circle grating is relatively simple: when viewed along the direction of the grating normal, the grooves appear parallel and equidistant.