Electrically Conductive And Infrared Transparent Thin Metal Film Coatings

Abstract

Electrically conductive (EC) and Infrared (IR) transparent thin metal film coatings for the 3 - 5 um and 8 - 12 um wavebands have been developed. Surface resistivity from 5 to 200 ohms/square have been studied. A transmittance value as high as 90% at 10.6 um has been achieved. The performance of these developed coatings are compared with the characteristics of the few IR transparent EC coatings reported in the literature. The fundamental difficulties in producing a highly transparent, wide optical bandwidth coating with low resistivity are discussed. The choice of a semiconductor or metal type EC coating are compared. The optical performance of these two types of IR EC coatings are calculated for equal electrical properties (surface resistivities). Induced transmission optical designs for both EC coating types are presented and the peak transmittance, and bandwidth achieved are compared. Measured results are compared with the calculated values. To date, the developed IR EC coatings have been vacuum deposited on ZnS, ZnSe, Ge, MgF2, Al203 and IR transmitting glass substrates materials. These coatings have also been deposited on a variety of flat optics and on a near hemispherical dome (9 diameter). Some present appli-cations and potential applications of these IR EC coatings are discussed. For example, a 3 - 5 um/millimeter wave aspheric beamsplitter has been produced. Electromagnetic Inter-ference (EMI) shielding of a MgF2 dome with a 3 - 5 um IR EC coating has been accomplished and verified by measurements.