GB305074A - Means for controlling the intensity of a beam of light for use, for example, in recording sound - Google Patents

Abstract

305,074. Eccles, W. H., Whitaker, A., and Gramophone Co., Ltd. Oct. 29, 1927. Light-valves.-Cristals which exhibit the Pockels effect are used in light-valves designed for operation at audio-frequency, so as to yield a photographic sound record. The change of illumination in ordinary Kerr cells is proportional to the square of the applied voltage, but in certain materials there exists a Pockels effect which produces a change of illumination directly proportional to the applied voltage, this effect preponderating over that previously mentioned. A crystal of Rochelle salt having the " hour-glass " structure shown at 7, Fig. 3, is cut along the plane 8 (shown by broken lines), the lower part 14 being discarded. The areas in which the Pockels effect is most marked are indicated at 9, 10. The crystal 1 is mounted as shown in Fig. 1 between two insulating tubes 2 which are closed at their ends by glass windows 3, filled with alcohol or other sui.table liquid, and provided with coaxial electrodes 4 connected to leads 5. The electric field is therefore mainly axial and parallel to the lightpencil which passes through the windows 3, but in a modification the crystal 1 may be mounted between parallel-plate electrodes, the light-pencil being then perpendicular to the electric field. The crystal ma be arranged between Nicol prisms and arranged to yield a photographic sound-record. The light employed may be monochromatic. The light-pencil may be made to traverse the cell repeatedly. The applied voltage is of telephonic frequency as distinct from modulated high frequency, the use of which is disclaimed, and may be superimposed on a direct-current polarizing voltage in the same or a different direction.