|
Chalcogenide glass with composition of Ge30As15Se55 was prepared for infrared imaging applications. Transmission wavelength range of the glass is from 1.8 micron to 16 micron, refractive index at 10 micron is about 2.50. The average transmittance between 8 and 12 micron is about 67%. Since the glass has low transmittance in the long-wave infrared (LWIR) band, it is necessary to coat the glass with antireflection coatings. The coatings will reduce the residual reflection from the surfaces of the glass. Compared with silicate glasses, the chalcogenide glass has low hardness. In harsh environment, the surface of the chalcogenide glass should be coated with hard coatings to improve its surface hardness. To meet the requirements posed by both optical and mechanical properties of the coatings, multilayer thin films including diamond-like carbon (DLC) thin film are applied. Typical structure of the multilayer thin film is Glass/ZnSe/BaF2/YF3(or SiO2)/DLC/Air. E-beam evaporation combined with unbalanced magnetron (UBM) sputtering is utilized to deposit the antireflection coatings. The DLC film is deposited with UBM sputtering, while other films are deposited with E-beam evaporation method. Apparatus of the coating system and the optical properties of the coatings in LWIR band are reported. |