Abstract: A method for restricting the mode of operation of long wavelength waveguide laser (FIG. 1) by introducing an approximate step function into the reflectivity of circular optical elements (19) used in such lasers. The preferred method is to grind off a portion of the optical coating (20) of the optical element (19) leaving a circular unground region (26) of high reflectivity having a diameter (D) of approximately 60% of the laser bore width (b) bounded by a ground region (28) of lower reflectivity. The method permits simple, inexpensive field modification of existing lasers.

Abstract: An improved optical block for use in a high brightness, full color image projection system of the type wherein high intensity (acrhomatic) projection light is modulated by a full color image composed of a plurality of monochromatic images applied to a plurality of polarization modulating light valves. A polarizer accepts the achromatic, unpolarized output of a high intensity source. Light of a preferred polarization orientation emergent therefrom is directed by the polarizer to a two level array of polarization-sensitive dichroic filters and wavelength-tuned biprisms. Input level dichroic filters separate the incoming unmodulated light into a plurality of component wavelength bands and direct each to a wavelength-tuned biprism. Each biprism directs the selected bandwidth of polarized light to the reflective surface of a light valve.