Antireflection structured surfaces for the infrared spectral region.

Antireflection structured (ARS) surfaces on GaAs substrates for application with normally incident, randomly polarized, 10.6-microm-wavelength radiation are designed and analyzed. Both one-dimensional (1-D) and two-dimensional (2-D) multilevel profiles are examined with special attention given to multilevel approximations of 1-D triangular and 2-D pyramidal profiles. The 1-D profiles are designed by using second-order effective medium theory (EMT), as we have found zeroth-order EMT to be insufficient when ARS surfaces are designed for use with optically dense materials, e.g., most materials used in the infrared spectral region. We analyze both 1-D and 2-D profiles by using rigorous coupled-wave analysis and find that the more levels the profile contains, the better the ARS surface's response to bias angles, wavelength detunings, and errors in etch depth. Although both 1-D and 2-D profiles can efficiently suppress reflections for unpolarized light, 2-D gratings are advantageous when randomly polarized light is of interest.