From modeling to fabrication of double side microstructured silicon windows for infrared gas sensing in Harsh environments

Commercial infrared windows used for gas sensing in the mid-IR range usually possess an anti-reflective coating. Those coatings can normally not withstand harsh environments, particularly not high temperatures. With a simple “3-step” fabrication process, high temperature resistant silicon windows (Ø1") were manufactured. The windows show high temperature resistant sub-wavelength anti-reflective surface microstructures on both side faces. Thus, a peak transmittance of 100% for a defined main wavelength (5 μm) and more than 90 % average transmittance for the wavelength range of 5-7 μm was achieved. The modeling of the anti-reflective microstructures, their fabrication process and final transmittance analysis of the windows is discussed.