Sol-gel optical coatings for lasers, 2

There are three basic types of antireflective (AR) coatings. The first is a single-layer coating in which the coating index is equal to the square root of the index of the substrate, assuming air is the external medium. The second type is a system of two or more layers of different indexes. The third type is a graded-index system, where the index is uniformly and continuously graded from the substrate to the external medium. Low reflection ranges from narrow for the single-layer to broad for the graded-layer and multilayered with a large number of layers. Four types of sol-gel AR coatings have been developed at CEL-V. They are based on single-layer or multilayer designs. They consist mainly of amorphous silica in the polymeric and/or colloidal state, combined in certain cases with other metallic oxides, binders, fillers, hydrophobic and lubricating agents, and adhesion promoters. These antireflective sol-gel-derived optical coatings have been prepared and tested for the proposed French megajoule neodymium-glass laser.