The ultraviolet groove efficiency for a holographically ruled diffraction grating with a trapezoidal profile has been measured. The efficiencies for the ±1 and the zero orders are in good agreement with those derived from scalar theory. The ±1 orders have equal efficiency as a function of wavelength. The peak of the sum of fitted groove efficiency functions is 76%, a level that is competitive with the groove efficiency of a mechanically blazed grating. We suggest that a normal-incidence grating mount with detectors at both orders will offer a system with twice the efficiency and provide a built-in redundancy. We discuss design considerations for reducing astigmatism equally in both orders in such dual-order mountings.
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