Optical coating for reflecting visible and longer wavelength radiation

Abstract

A coated reflector reflective of radiation having two different wavelengths over a wide range of incidence angles, including grazing incidence angles. The coated reflector can be employed in a waveguide for laser radiation useful for medical or other applications, such as a combined HeNe and CO.sub.2 laser beam. Preferably, the coated reflector includes a metal substrate and a multi-layer stack thereon, the multi-layer stack consists of alternating dielectric layers of high and low refractive index material, each pair of adjacent high and low index layers of the stack has a combined matched optical thickness substantially equal to an incident short (e.g., visible) wavelength multiplied by a factor M/2, and the total matched optical thickness of the stack is substantially equal to (2N-1).lambda..sub.L /8, where M and N are positive integers and .lambda..sub.L is an incident long wavelength (such as the wavelength of a CO.sub.2 laser beam). Preferably, the substrate is silver, the high index dielectric is zinc sulfide, and the low index dielectric is yttrium fluoride or cerium fluoride. In other embodiments, the invention is a coated substrate having substantially parallel indentations along which it can be folded into a polygonal shape for use a waveguide.