Abstract: An apparatus for making aromatic heterocyclic polymeric fibers having enhanced compressive strength is disclosed. Individual polymeric fibers, while being made according to otherwise conventional methods, are full twisted as they are drawn from a spinnerette hole so that their internal fibrils and microfibrils become entangled. The twisting is performed before coagulation of the fibers. The entangled fibrils and microfibrils are believed to provide mutual support to adjacent fibrils/microfibrils to resist buckling under compression.

Abstract: An optical filter for blocking radiation of preselected wavelength is described which comprises a colloidal suspension of an optical medium and a multiplicity of microspheres of optical dimensions in a substantially regular three-dimensional array, the optical medium and microspheres comprising materials having matched indices of refraction in the absence of incident radiation, but at least one index of which varies nonlinearly with incident electric field whereby an index mismatch and resulting Bragg diffraction within the suspension is produced by incident radiation of the selected wavelength.