Fabrication of Fresnel lenses operating in long infrared

We present the technological processes required to fabricate silicon Fresnel lenses for long infrared spectral range. The Fresnel lenses operate as image corrector in standard long infrared imaging systems and its optical surface consists of sixteen discrete levels. The Fresnel lenses are fabricated using four photolithographic processes, each process being followed by deep reactive ion etching. The characterization by the white light interferometry reveals that the geometrical parameters of the fabricated Fresnel lenses are in good agreement with the design specification. The atomic force microscopy determinations show a low value of the roughness indicating a high quality of the optical surfaces.