Surface relief gratings can have high diffraction efficiencies in the “scalar” domain where the grating period is more than about ten times the illumination wavelength, as well as in the Bragg resonance domain where the grating period approaches the illumination wavelength and only three diffraction orders +1st, 0, -1st are nonevanescent. The resonance domain is of particular interest for many applications, and extensive numerical methods have been developed for analyzing and optimizing the grating parameters and trade-offs [1,2]. Typically, such numerical methods are rather cumbersome and time consuming.