A rugate filter coating for reflecting at least a portion of at least one electromagnetic wavelength band, the filter comprising a transparent coating on a substrate, the coating having an incrementally varying refractive index of refraction depth, with each of the increments having a constant a constant...http://www.google.com.au/patents/US6256148?utm_source=gb-gplus-sharePatent US6256148 - Rugate filter and method of making same
