| 摘要 |
PURPOSE:To prevent the loss the quantity of light at an exit slit by using a concave mirror which has difference radii of curvature in a meridian plane and a sagittal plane as the main mirror of a spectral system which has uses a plane diffraction grating, and removing astigmatism. CONSTITUTION:The spectral system of an Evert mounting consists of the plane diffraction grating 3, main mirror 2, entrance slit 1, and exit slit 4. The main mirror 2 is composed of an aspherical mirror whose radii R and rho in the meridian plane and sagittal plane are not equal. Consequently, three specific arithmetic expressions showing image-formation conditions in a wavelength divergence direction among distances (r) and (r') between the entrance slit 1 and exit slit 4, and main mirror 2, distances D and D' between the main mirror 2 and difraction grating 3, and angles theta and theta' of incidence and reflection of an incident beam on and from the main mirror 2 are satisfied at the same time, so the astigmatism is removed, thereby preventing the loss of the quantity of light at the exit slit 4. |
