Hardened optical windows with anti-reflective, reflective, and absorbing layers for infrared sensing systems

A LIDAR system comprising:

• an electromagnetic radiation emitter and sensor that emits electromagnetic radiation having a wavelength of 1550 nm;
• and
• a window in the path of the electromagnetic radiation, the window comprising:
• a substrate that comprises a refractive index, a first surface, and a second surface, the first surface and the second surface being primary surfaces of the substrate;
• a layered film disposed on the first surface of the substrate, the layered film comprising alternating layers of one or more higher refractive index materials and one or more lower refractive index materials, each of the one or more higher refractive index materials and the one or more lower refractive index materials having a refractive index, and the refractive index of the one or more higher refractive index materials being greater than the refractive index of the one or more lower refractive index materials;
• and
• a maximum hardness, measured at the layered film and by the Berkovich Indenter Hardness Test, of at least 8 GPa,
• wherein the quantity, the thicknesses, and materials of the alternating layers of the layered film are configured so that the window has:
• an average percentage transmittance of greater than 75% for electromagnetic radiation having a wavelength of 1550 nm at normal or near normal incidence;
• and
• an average percentage reflectance of less than 10% for electromagnetic radiation having a wavelength of 1550 nm at any angle of incidence within the range of 0° to 8°, and
• wherein the one or more lower refractive index materials comprises SiO2, and wherein a layer of SiO2 is disposed directly onto the first surface of the substrate.