Broadband antireflection gratings for glass substrates fabricated by fast atom beam etching

We fabricated a two-dimensional subwavelength-structured (SWS) surface on a glass substrate. The SWS surface was patterned by electron-beam lithography and etched by an SF6 fast atom beam. The SWS surface consisted of tapered gratings with a 150 nm period and a 150 nm deep groove. The reflectivity at wavelengths from 400 nm to 2000 nm was measured and compared with the results calculated on the basis of rigorous coupled-wave analysis. At wavelengths from 400 nm to 800 nm, the reflectivity of the glass surface decreased to 1% from the original value of 5% of the glass substrate. The reflectivity was also examined as a function of the incident angle by using He-Ne laser light.