Interference filters for the ultraviolet and the surface plasmon of aluminum

It is shown that (Al-MgF2)-interference filters of better performance than have been predicted and obtained previously are possible in the uv below 2500 Å. Experimental results are given for conventional filters of first and higher order and for new filter designs that use multilayer structures for the two mirrors of the filter. All discrepancies between theoretical and experimental results are explained by a coupling of light into the surface plasmon of aluminum via a surface roughness of the MgF2 films. © 1974 Optical Society of America.