Assymmetric double pass grating monochromator

Claim 1

In an asymmetric, double pass, grating monochromator, the combination comprising a. means forming entrance, intermediate and exit slits to define successive sections of the monochromator operable to isolate a band of wavelengths with high and low limits, b. a grating in the beam path between the entrance and exit slits and operable to disperse a beam of radiation incident thereon both prior and subsequent to radiation passage through the intermediate slit, the grating having rulings, c. means to rotate the grating about a first axis, which is parallel to the grating rulIngs, d. the entrance and exit slits symmetrically disposed at opposite sides of a plane bisecting and normal to a line extending between the entrance and exit slits, said plane also passing through the intermediate slit, and e. said axis having intersection with said plane and extending at an angle Psi relative to a normal to said plane that passes through said intersection, the angle Psi characterized in that spectral overlap is substantially eliminated and defined as having the approximate value arc sin S/R where S one-half the length of said line extending between the entrance and exit slits, and R the distance between said intersection and the center of either of the entrance and exit slits.