Six-spectral antireflection coating on zinc sulfide simultaneously effective for the visible, near-IR, and long wavelength IR regions

In recent years, multi-spectral optical system is steadily growing popularity due to miniaturization and multi-function of optical system. Antireflection coatings is critical important in multi-spectral device working in the wavelength region of 0.5-10 mu m since optics of high refractive index materials are used. A six-spectral antireflection coating on multispectral zinc sulfide substrate, which is suitable for the wavelength range of 0.5-10 mu m, has been designed, fabricated and characterized. The six-spectral antireflection coating is composed of 29-layer alternative stacking high-index layer of zinc sulfide and low-index coating material of ytterbium fluoride, which deposits by thermal evaporation. In order to overcome the stress problem in the coating, the maximum layer thickness is restricted about 0.6 mu m. This coating conforms to environmental stability standards and shows 94% transmission at 0.532 mu m, 97% transmission at 1.064 mu m and over 98% transmission at 2.1 mu m, 3.9 mu m, 4.8 mu m and 9.5 mu m.