Wideband anti-reflection coating - with five layers of high, medium and low refractive index materials

A wideband anti-reflection coating, for reducing reflection from low refractive index substrates in the visible to near-IR range, consists of five layers of constant optical thickness comprising one or more high refractive index layers (H), one or more medium refractive index layers (M) and one or more low refractive index layers (N). The novelty is that the optical thicknesses are equal to one-quarter of the light wavelength in the 620-660 nm range and that the layers comprise: between a glass substrate of n (refractive index at 550 nm) = at least 1.45 and air of n = 1.0003, (i) a first M layer of n = 1.55-1.75, (ii) a second H layer of n = 1.80-2.10, (iii) a third H layer of n = 2.00-2.30, (iv) a fourth H layer of n = 1.75-2.00 and (v) a fifth N layer of n = max. 1.50. USE/ADVANTAGE - The coating is esp. useful for optical transmission elements of glass, plastics or crystal. It ensures a residual reflection of less than 0.9% over the 450-1100 nm spectral range including the laser wavelength of 1.06 microns, employs conventional materials of constant optical layer thickness and is inexpensive to produce.