Dme Corporation

Michel Letellier

A process for the deposition, on an optical substrate, of an antireflection coating capable of being engraved. In the process, metal is evaporated in a reactive atmosphere within the enclosure of an evaporator under vacuum and then deposited on the substrate. Previously cleaned substrates are disposed within the enclosure, which is then evacuated until a pressure of at most 1.5 .mu.Pa (10.sup.-8 torr) is obtained. Pure oxygen is injected at a regulated throughput in such a manner that the pressure is within the range of from 2 to 4 mPa, preferably 3 mPa (2.times.10.sup.-5 torr). A heated boat which is disposed within the enclosure and contains chromium is unmasked. The chromium evaporates at a temperature such that a coating of chromium oxide grows in thickness on the substrates at a rate of 0.1 to 0.5 nm per second, preferably 0.2 nm per second. The boat is masked when the coating of chromium oxide has reached a thickness corresponding to the first extinction in specular reflection at substantially normal incidence. The rate of growth is controlled with reference to the resonance drift of a quartz resonator which is also subjected to the deposit of chromium oxide. The extinction is monitored in white light at 3400.degree. K. on a control substrate which has previously been metallized.

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Paris, France

Michel Letellier