Diffraction pattern of self-supporting transmission gratings

Self-supporting transmission gratings suitable for the soft x-ray and extreme ultraviolet must be reinforced by support structures which, if regularly placed, tend to produce undesirable artifacts in the diffraction plane. Because these artifacts appear in the neighborhood of the principal maxima and can be substantial in magnitude, they may confuse the spectrum. Methods are described whereby these unwanted diffraction effects are much reduced or eliminated. In one method, the members of the support structure parallel to the grating slits are placed in a random pattern so that on the average the coherence of the support structure is drastically reduced everywhere. In a second method, these support structure members are distributed pseudorandomly in such a manner that the diffraction pattern of the support structure is completely removed from the diffraction plane. A third method is investigated in which the pseudorandom placement of supports is organized into a repeated pattern, which may be easier to manufacture than the configurations of the first two methods.