Quantitative comparison of the general Sweatt model and the grating equation.
When using the general Sweatt model for ray tracing diffractive optical elements (binary optics, holographic optical elements, etc.), lens designers must choose an index of refraction that is sufficiently high to avoid significant errors in the ray trace. We derived two new criteria for a sufficiently high index of refraction. To avoid significant errors, the index must satisfy these two new criteria in addition to Sweatt's originally suggested criterion. In almost all cases the new criteria require a higher index than Sweatt's original criterion.
Farn
M W
MW