AlN and MgO thin-layer coatings on the bendable polymeric substrates as selective filters for IR and THz spectral ranges

Abstract

Thin AlN and MgO poly- or nano-structured layers were synthesized on bendable polymeric substrates using the helicon-arc ion-plasma method. They can be used as filters to block infrared (IR) radiation from civil and military objects. To suppress IR radiation within the range λ ~ 7.5…25 µm, where most of the radiation power from objects with the temperature T ~ 300…400 K is concentrated, we have used AlN and MgO thin layers (d ~ 1.5…10 μm) that have the Restrahlen bands within the spectral range indicated above. The optical, structural properties and chemical composition of AlN and MgO films on the Mylar or Teflon substrates have been investigated. These filters demonstrate blocking characteristics for masking the thermal image of objects heated to a temperature of 300…400 K in the IR spectral range. At the same time, they are well transparent in the microwave and THz spectral ranges (transparency τ up to ≈ 80…85%). Moreover, thin Mylar films with AlN coatings are transparent in the visible range. Using the combined coatings of AlN with high thermal conductivity (110…140 W/m·K in the polycrystalline form) for heat withdraw to the periphery or air and MgO coatings, one can suppress IR radiation by more than 90% within the spectral range λ = 7.5…25 μm.