Dual Blaze Gratings

Two (or more) gratings with different groove spacings may be combined in this way. Since the dispersion from each groove pattern will differ, though, the spectra will generally be imaged separately. An optical component of this nature would serve as two distinct gratings whose positions and orientations are fixed relative to each other. Gratings with the same groove spacing, however, may be combined in this way to form a component that behaves like a single grating, but with an efficiency curve formed by the weighted average of the efficiencies of the sections (weighted by the illuminated areas of each section). Such dual-blaze gratings can provide efficiency curves that are not achievable with conventionally produced gratings, due to limitations in the available groove profiles. The relative areas of the two sections can be chosen to tailor the efficiency behavior of the entire grating.

Dual-blaze gratings are made by carefully replicating submasters from two different gratings together to produce a dual-blaze submaster, which itself is replicated using conventional means. Gratings made in this way have exhibited wavefront distortions of λ/4 or less, and exhibit efficiency characteristics that cannot be obtained from single ruled gratings, in that their efficiency curves have lower and broader peaks (see Figure 5-3).