Patent GB-514860-A (GB)
Title: Improvements relating to light-polarizing material
IPC: G02B5/30
Filed: 1938-05-17
Abstract: 514,860. Optical polarizers. LAND, E. H. May 17, 1938, No. 14752. Drawings to Specification. [Class 97 (i)] A light polarizing body comprises a suspension of optically oriented, uniaxial or biaxial, birefringent particles embedded in a light-transmitting, isotropic or birefringent medium having a refractive index substantially equal to one of the refractive indices of the particles; and if the medium is birefringent, the other two refractive indices should be-unequal. The body transmits substantially all one component of an incident beam and' a high percentage of the other; and one component may be transmitted as a non- diffused beam and the other as a highly diffused beam in a perpendicular plane, e.g., for motor headlights, the non-diffused beam illuminating the distant roadway, and the diffused beam the immediate vicinity, in which case the driver of an approaching vehicle equipped with a polarizer as described in Specification 412,179 could eliminate the non-diffused glare or the diffused beam from the headlight. By controlling the shape and number of particles in the path of the beam, the diffused beam may be caused to emerge as a depolarized beam, or even as a polarized beam whose plane of polarization coincides with that of the non-diffused component, rendering further elimination possible. A combination of the material of the present invention with that of Specification 412,179 may be used to alter the degree of diffusion of a transmitted beam. The particles may be oriented by introducing them into the medium while this is plastic, and then applying mechanical stress, as by flowing, pouring, rolling or stretching the medium. or extruding it through an orifice, or by applying an electric or magnetic field to which the particles are responsive. The action of bodies composed of uniaxial of biaxial particles on incident beams is discussed in relation to incidence of the beam, the lay-out of the' crystals and the correspondence of their refractive indices with those of the medium. The Specification gives numerous examples of uniaxial and biaxial crystals and of suspending media, with their refractive indices. The media include cellulosic materials, resins, glass and other vitreous media, and solvents and plasticizers which have no action on the particles may be included therein. The bodies may be made to function throughout a wide band of wavelengths, e.g., throughout the visible spectrum, or the infra-red, or ultra-violet; or through all such wave-lengths. The preparation of a body containing needles of potassium nitrate in a mixture of cellulose acetate, dimethylphthalate and the material known as "Santolite" is described, acetone being used as solvent. The preparation of a body containing urea crystals in cellulose acetate propionate, ethyl acetate, and dimethylphthalate is also described, methanol being used as solvent. The body may be enclosed between light-transmitting sheets as of glass; and with suitable selection of plasticizer may be waterproof. When the body is to be subjected to high temperatures, the plasticizer should be omitted.