Plasma impulse chemical vapour deposition—a novel technique for the production of high power laser mirrors

Abstract

Chemical vapour deposition (CVD) methods are known to be most advantageous for the production of very high quality optical materials ( i.e. performs for low loss fibres or high damage threshold, and reflection coatings on thin fibres). It is also well known that plasma-enhanced CVD methods show improved deposition efficiencies. Pulsed microwave plasmas (2.45 GHz) are used to realize interference filters with very high laser damage threshold as well as high reflection. The impact of the coating temperature on the layer quality is discussed. The high deposition rate together with the almost monolayer-by-monolayer growth control in the pulsed plasma mode is suitable for producing extreme small-band, high reflection coatings, which have no harmonics. By almost individual shaping of the refractive index distribution within one λ/4 layer a new degree of freedom in the design of these coatings has been accomplished. The theoretical background as well as experimental results are discussed.