Using the compensating effect for Rayleigh anomalies to design a type of broadband mid-IR grating.

We suggest and numerically demonstrate a specific design method of broadband mid-IR echelette grating. The method, which applies the compensating of the efficiency blaze in TM-plane polarization to Rayleigh anomalies, is called compensating effect method. This idea allows the grating designer to realize fully the considerable advantages of this type of echelette grating with an apex angle 90 degrees and a blaze angle 19.47 degrees , especially, it can be fabricated easily with conventional (holographic and ruled) techniques. Its diffraction efficiency in unpolarized light has a minimum value of 40%. The cases of Littrow mount and off-Littrow mount are both discussed.