Hardened optical windows with anti-reflective films having low visible reflectance and transmission for infrared sensing systems

A window for a sensing system comprising:

• a substrate comprising a first surface and a second surface, the first surface and the second surface being primary surfaces of the substrate;
• a first layered film disposed on the first surface of the substrate, the first layered film comprising alternating layers of one or more higher refractive index materials and one or more lower refractive index materials, wherein refractive indices of the one or more higher refractive index materials of the first layered film are higher than refractive indices of the one or more lower refractive index materials of the first layered film;
• a second layered film disposed on the second surface of the substrate, the second layered film comprising alternating layers of one or more higher refractive index materials and one or more lower refractive index materials, wherein refractive indices of the one or more higher refractive index materials of the second layered film are higher than refractive indices of the one or more lower refractive index materials of the second layered film;
• and
• a maximum hardness, measured at the first layered film and by the Berkovich Indenter Hardness Test, of at least 8 GPa,
• wherein the quantity, the thicknesses, number, and materials of the alternating layers of the first and second layered films are configured so that the window has:
• an average percentage transmittance, calculated over a 50 nm wavelength range of interest between 1400 nm and 1600 nm, of greater than 90% for light incident on the first surface and the second surface at angles of incidence of less than or equal to 15°;
• an average reflectance, calculated over the 50 nm wavelength range of interest between 1400 nm and 1600 nm, of less than 1% for light incident on the first surface and the second surface at angles of less than or equal to 15°;
• and
• an average percentage transmission, calculated from 400 nm to 700 nm, of less than 5% for light incident on the first surface and the second surface at angles of incidence of less than or equal to 15°.