Abstract: An optical filter uses a multi-layer, stack of alternating dielectric layers (16, 18) of different refractive indices, a dielectric spacer layer (20) and metal layer (21), to achieve a narrow overall absorption bandwidth, with high reflectance upon either side. A tunable (optical) filter variant uses a dielectric stack and spacer coating of spatially-varying thickness, that is a coating of depth varying, say linearly and/or circularly, according to position across an absorbent layer or substrate, whereby, at different positions on the surface, a different wavelength is absorbed. A tunable laser (35) uses opposed tunable filters (26, 28) bounding a lasing medium (38), such as CO2 gas, for selective variable stimulated emission of radiation (39).

Abstract: A filter system for reflectively blocking laser radiation in the visible spectrum includes a multilayer interference structure arranged for reflectively blocking a continuous band of wavelengths including the laser radiation and transmitting other wavelengths in the visible spectrum. The filter system is arranged to control transmission of the other wavelengths of the visible spectrum such that the filter system has an essentially neutral transmission color and maximum photopic transmission consistent with the band of wavelengths reflectively blocked.

Abstract: A polarization preserving reflector for reflecting an incident beam of monochromatic radiation, said beam having a polarization configuration and an angle of incidence. The polarization preserving reflector comprises a substrate; a highly reflective layer positioned adjacent to said substrate; and at least two thin film optical layers one of which being positioned adjacent to the highly reflective layer, one of the thin film optical layers having a high refractive index and another having a low refractive index, for maintaining the incident polarization configuration while producing a high reflectance upon reflection of the beam therefrom in a wide range of the angle of incidence from approximately zero degrees to 75 degrees.

Abstract: A broad band phase shifting system, having a fixed angle of phase retardation, has at least one broad band reflecting means in the system. The broad band reflecting means also has an angle of phase retardation, with the angle of phase retardation of the reflecting means less than the fixed angle of phase retardation of the system.