Barr & Stroud Limited

The Secretary of State for Defence in Her Britannic Majesty's Government

Christopher J Kelly

Keith Loder Lewis

Brian C Monachan

Michael A Biagi

An optical filter comprises a multilayer coating adherent to a substrate, the coating comprising at least four superimposed layer collections. Each layer collection has ordered first, second and third layers of which the first and third layers are made of a first material and are 0.6 quarter wavelengths thick whereas the second layer is made of a second material and is 6.8 quarter wavelengths thick. One of these materials has a high refractive index in the range 1.9 to 2.5 whilst the other of these materials has a low refractive index in the range 1.3 to 1.7. The preferred high index material is zinc sulphide and the preferred low index material is thorium fluoride. The optical filter is generally transmissive except in a number of narrow waveband regions which include respective known laser wavelengths.

Optical filters with coatings transmissive in narrow waveband regions

Infrared transmitting optical components having a wide variety of substrates (e.g. ZnS, ZnSe, Ge, Si, SiO.sub.2) are disclosed all with an optical coating of boron phosphide (BP). The boron phosphide may be a single layer coating or one layer of a multilayer coating in which case it is preferably the penultimate layer. Coated components are provided which are very low in absorption, which are operable at high temperatures with minimal transmission loss, and which are transmitting in two IR wavebands. The boron phosphide layer is deposited by plasma-assisted chemical vapor deposition at a temperature in the range 300.degree.-500.degree. C. preferably using feedstock gases which are hydrogen-fee. Boron phosphide coatings of up to 40 .mu.m in thickness have been achieved.

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Hyndland, United Kingdom

Christopher J Kelly