Design and preparation of UV-visible-shortwave near infrared cut-off and mid-infrared antireflection coating

In recent years, mid-infrared window is steadily growing popularity due to the development of mid-infrared technology. Mid-infrared antireflection coating with UV-vis-shortwave near infrared cut-off is critical important in the infrared detector, which can improve quality of signal in mid-infrared and avoid noise introduced by non-working wavelength band. Based on electron beam evaporation technique with argon plasma assistance, a mid-infrared antireflection coating with UV-vis-shortwave near infrared cut-off on oxyflouride substrate, has been designed, fabricated and characterized. The coating on the first side of substrate is composed of 7-layer alternative stacking high-index layer of germanium and low-index coating material of magnesium fluoride. The coating on the second side of substrate is composed of 2-layer alternative stacking high-index layer of alumina and low-index coating material of silicon oxide. This coating shows below 1% average transmittance from 300 nm to 900 nm and above 92 % average transmittance from 3.7 um to 4.8 um in mid-infrared region. The error analysis shows that thickness errors are the main reasons for the deviations between theoretical design and experimental results. In addition, the adhesion strength of the coating is quantitatively characterized by scratch-adhesion test.