Design of blocking filters of any narrow bandwidth.

A design approach is described to achieve spectral blocking filters of any spectral width and optical density for narrow blocking bands. The ratio of the thickness of the high-index material to the low-index material in the layer pairs is adjusted to obtain the desired bandwidth in the first-harmonic reflection band. The number of layer pairs is adjusted to provide the required optical density. Equations are provided for estimating the ratios and number of layer pairs needed to achieve a given bandwidth and optical density. This approach can be useful for laser line blocking filters, night vision filters, and other general applications.