Optical element

An optical element, comprising:

• a substrate;
• and
• a coating supported by the substrate,
• wherein:
• the coating comprises, in order moving away from the substrate, a first layer, a second layer, a third layer, a fourth layer, and a fifth layer,
• the second layer comprises an inorganic fluoride having a low refractive index at a wavelength in the ultraviolet range;
• the third layer comprises an inorganic oxide;
• the fourth layer comprises an inorganic fluoride;
• and
• the fifth layer comprises an inorganic oxide.

An optical element, comprising:

• a substrate;
• and
• a coating supported by the substrate,
• wherein:
• the coating comprises at least five layers;
• the at least five layers comprise alternating layers of inorganic oxide and inorganic fluoride materials;
• of the layers comprising an inorganic oxide, the layer furthest from the substrate has a first refractive index at a wavelength in the ultraviolet range;
• of the layers comprising an inorganic fluoride, the layer closest to the substrate has a second refractive index at the wavelength in the ultraviolet range;
• and
• the first refractive index is greater than the second refractive index.

An optical element, comprising:

• a substrate;
• and
• a coating supported by the substrate,
• wherein:
• the coating comprises at least five layers;
• the at least five layers comprise alternating layers of inorganic oxide and inorganic fluoride materials;
• of the layers comprising an inorganic oxide, the layer closest to the substrate has a first refractive index at a wavelength in the ultraviolet range;
• of the layers comprising an inorganic fluoride, the layer second closest to the substrate has a second refractive index at the wavelength in the ultraviolet range;
• and
• the first refractive index is greater than the second refractive index.