  We used two novel approaches to produce sub-wavelength structure (SWS)
anti-reflection coatings (ARC) on silicon for the millimeter and sub-millimeter
(MSM) wave band: picosecond laser ablation and dicing with beveled saws. We
produced pyramidal structures with both techniques. The diced sample, machined
on only one side, had pitch and height of 350 $\mu$m and 972 $\mu$m. The two
laser ablated samples had pitch of 180 $\mu$m and heights of 720 $\mu$m and 580
$\mu$m; only one of these samples was ablated on both sides. We present
measurements of shape and optical performance as well as comparisons to the
optical performance predicted using finite element analysis and rigorous
coupled wave analysis. By extending the measured performance of the one-sided
diced sample to the two-sided case, we demonstrate 25 % band averaged
reflectance of less than 5 % over a bandwidth of 97 % centered on 170 GHz.
Using the two-sided laser ablation sample, we demonstrate reflectance less than
5 % over 83 % bandwidth centered on 346 GHz.
