High performance Notch Filter Coatings produced with PIAD and Magnetron Sputtering

For Notch Filters, Rugate designs with a small index contrast and apodisation are well known in the literature. The required deposition of gradient index layers or so called flip flop structures is very complicated and difficult to manufacture. Higher order H/L stacks of coating materials with high index contrast result in very thick layer stacks. In our approach we replace the second refractive index by equivalent layers consisting of H/L materials with high index contrast. This leads to a combination of thick (>100nm) and very thin layers. Stable coating processes with dense layers are strict requirements. Another challenge is the accurate thickness control of very thin layers in the nanometer range. Single notch filters were produced with PIAD and broad-band optical monitoring. The most challenging filters were demonstrated with magnetron sputtering and monochromatic optical monitoring. Some outstanding results of single and multiple notch filter coatings will be presented.