Abstract: A waveguide including a folded, coated reflector highly reflective of radiation having two different wavelengths over a wide range of incidence angles, including grazing incidence angles. The waveguide can be employed for guiding laser radiation useful for medical or other applications, such as a combined HeNe and CO.sub.2 laser beam. In some embodiments, the invention is a hollow waveguide formed by folding a flat, coated substrate into a polygonal shape. Because the coated substrate is folded, rather than rolled into a cylindrical tube, the bending stress on the coating is concentrated at the corners of the polygonal waveguide rather than distributed over the waveguide's entire surface. Although the coating may crack at the corners of the waveguide's polygonal cross-section, the flat surfaces between the waveguide edges will be intact, and the cracks in the corners will have an insignificant effect on waveguide performance.

Abstract: A dichroic optical filter including a substrate that is substantially transparent to visible radiation, and an oxide semiconductor layer on the substrate for reflecting an infrared wavelength (such as an infrared treatment beam wavelength). An example of a suitable oxide semiconductor for reflecting a treatment beam from a CO.sub.2 layer is indium tin oxide. Preferably, the filter includes a specially designed multilayer coating on the oxide semiconductor layer to enhance the reflection of infrared and longer wavelength radiation. This multilayer coating includes alternating quarter-wave layers of high and low refractive index materials, each having an optical thickness substantially equal to a quarter-wavelength of infrared radiation to be reflected.

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).

Abstract: A dichroic optical filter including a substrate that is substantially transparent to visible radiation, and an oxide semiconductor layer on the substrate for reflecting an infrared wavelength (such as an infrared treatment beam wavelength). An example of a suitable oxide semiconductor for reflecting a treatment beam from a CO.sub.2 layer is indium tin oxide. Preferably, the filter includes a specially designed multilayer coating on the oxide semiconductor layer to enhance the reflection of infrared and longer wavelength radiation. This multilayer coating includes alternating quarter-wave layers of high and low refractive index materials, each having an optical thickness substantially equal to a quarter-wavelength of infrared radiation to be reflected.