Figure vsg.6 : Flight and VSG Grating Diffraction Properties. The diffraction efficiency of a grating depends on (is modeled by) the grating bar shape. Here, each facet is represented as a point plotted in bar parameter space: the average bar height and the bar full width at half maximum. The width is expressed relative to the period, hence it is the bar "duty cycle". All but one of the VSGs plotted here fall into the region generally representative of the flight gratings; the exception is grating HE2423 (width/period ~ 0.7, height ~ 4000 A) which is well outside the flight HEG region.
For reference, the X-GEF reference grating parameters are as follows: MX078: 4400., 0.615; HX220: 4000., 0.675.