Anti-reflective coating for optical windows and elements

A multilayer anti-reflective coating for a substrate, comprising:

• (a) a first layer having a refractive index n1, where n1<1.4, and an optical thickness of (0.23±5%) λo nm, which in expanded form is a range of (0.23-5% of 0.23) λo nm to (0.23+5% of 0.23) λo nm, where λo is a wavelength in the infrared range;
• (b) a second layer adjacent to the first layer, the second layer having a refractive index n2, where n2≧1.8, and an optical thickness of (0.35±5%) λo nm, which in expanded form is a range of (0.35−5% of 0.35) λo nm to (0.35+5% of 0.35) λo nm, where λo is a wavelength in the infrared range;
• (c) a third layer adjacent to the second layer, the third layer having a refractive index n3, where 1.4≦n3<1.6, and an optical thickness of (0.06±10%) λo nm, which in expanded form is a range of (0.06−10% of 0.06) λo nm to (0.06+10% of 0.06) λo nm, where λo is a wavelength in the infrared range;
• and
• (d) a fourth layer adjacent to the third layer, the fourth layer having a refractive index n4, where n4≧1.8, and an optical thickness of (0.06±10%) λo nm, which in expanded form is a range of (0.06−10% of 0.06) λo nm to (0.06+10% of 0.06) λo nm, where λo is a wavelength in the infrared range;
• the anti-reflective coating having a coating order of first layer/second layer/third layer/fourth layer, with the first layer being the outermost layer relative to the substrate.

An optical window, comprising:

• (i) a glass or glass-ceramic substrate transmissive to light;
• and
• (ii) a multilayer anti-reflective coating applied on the substrate, the multilayer anti-reflective coating comprising:
• (a) first layer having a refractive index n1, where n1<1.4, and an optical thickness of (0.25±5%) λo nm, which in expanded form is a range of (0.25−5% of 0.25) λo nm to (0.25+5% of 0.25) λo nm, where λo is a wavelength in the visible light range;
• (b) a second layer adjacent to the first layer, the second layer having a refractive index n2, where n2≧1.8, and an optical thickness of (0.5±5%) λo nm, which in expanded form is a range of (0.5−0.5% of 0.5) λo nm to (0.5+5% of 0.5) λo nm, where λo is a wavelength in the visible light range;
• (c) a third layer adjacent to the second layer, the third layer having a refractive index n3, where 1.4≦n3<1.6, and an optical thickness of (0.1±5%) λo nm, which in expanded form is a range of (0.1−5% of 0.1) λo nm to (0.1+5% of 0.1) λo nm, where λo is a wavelength in the visible light range;
• and
• (d) a fourth layer adjacent to the third layer, the fourth layer having a refractive index n4, where n4≧1.8, and an optical thickness of (0.05±10%) λo nm, which in expanded form is a range of (0.05−10% of 0.05) λo nm to (0.05+10% of 0.05) λo nm, where λo is a wavelength in the visible light range;
• the anti-reflective coating having a coating order of first layer/second layer/third layer/fourth layer, with the first layer being the outermost layer relative to the substrate.

An optical window, comprising:

• (i) a glass or glass-ceramic substrate transmissive to light;
• and
• (ii) a multilayer anti-reflective coating applied on the substrate, the multilayer anti-reflective coating comprising:
• (a) a first layer having a refractive index n1, where n1<1.4, and an optical thickness of (0.23±5%) λo nm, which in expanded form is a range of (0.23−5% of 0.23) λo nm to (0.23+5% of 0.23) λo nm, where λo is a wavelength in the infrared range;
• (b) a second layer adjacent to the first layer, the second layer having a refractive index n2, where n2≧1.8, and an optical thickness of (0.35±5%) λo nm, which in expanded form is a range of (0.35−5% of 0.35) λo nm to (0.35+5% of 0.35) λo nm, where λo is a wavelength in the infrared range;
• (c) a third layer adjacent to the second layer, the third layer having a refractive index n3, where 1.4≦n3<1.6, and an optical thickness of (0.06±10%) λo nm, which in expanded form is a range of (0.06−10% of 0.06) λo nm to (0.06+10% of 0.06) λo nm, where λo is a wavelength in the infrared range;
• and
• (d) a fourth layer adjacent to the third layer, the fourth layer having a refractive index n4, where n4≧1.8, and an optical thickness of (0.06±10%) λo nm, which in expanded form is a range of (0.06−10% of 0.06) λo nm to (0.06+10% of 0.06) λo nm, where λo is a wavelength in the infrared range;
• the anti-reflective coating having a coating order of first layer/second layer/third layer/fourth layer, with the first layer being the outermost layer relative to the substrate.