Blazed binary diffractive gratings with antireflection coating for improved operation at 10.6 μm

We report on the design fabrication and characterization a 3-period grating composed of subwavelength ridges of progressively varying widths for operation at 10.6 µm. The grating is blazed into the first transmitted order (an efficiency of 80% is measured) under TM polarization and over a broad range of angles of incidence. The fabrication involves contact photolithography, reactive-ion etching, and an evaporation deposition over the etched structure. The result validates the use of photolithography, a low-cost technology, for the manufacture of efficient blazed binary diffractive elements for thermal imaging (the 8- to 12-µm IR band).