Fabrication of multilevel silicon diffractive lens at terahertz frequency

In this paper, we fabricated an anisotropically etched multilevel silicon diffractive lens. The operating frequency and focal length of the lens are 2.52 THz and 15 mm, respectively. Both 4- and 16-level lenses have been realized. The total etch depth and size of the lenses are 49 $mu{hbox{m}}$ and 45 mm $times$45 mm. Positive tone thick resist AZ 4562 was used as a mask material for dry etching the high resistivity silicon substrate. We have characterized the lens using a high power continuous wave far infrared laser operating at 2.52 THz. The measured results show good agreement with the designed specifications