Patent GB-1066655-A (GB)
Title: Laser systems
IPC: H01S3/101
Filed: 1965-10-06
Abstract: 1,066,655. Lasers; cathode - ray tubes. INTERNATIONAL BUSINESS MACHINES CORPORATION. Oct. 6, 1965 [Nov. 20, 1964], No. 42495/65. Addition to 1,055,840. Headings H1D and H1C. In a laser in which an active element 5, e.g. ruby, positioned between mirrors 7, 23 serves as a lens so that light from any point on one mirror is focused at a respective point on the other mirror, an output beam controllable as to its direction and intensity is obtained by selectively directing an electron beam 31 towards a point on one of the mirrors. As shown in Fig. 1, the optical cavity formed by spherical mirror 7 and plane mirror 23 includes a 45 degrees polarizer 27, an optical retardation plate 26 which introduces a relative phase delay between horizontal and vertical polarization components of light passing through, and a KDP (potassium dihydrogen phosphate) layer which exhibts an electrooptical effect in the presence of a<SP>11</SP> electric field. The KDP layer has a stannou<SP>s</SP> oxide (SnO) coating 25 connected to ground on one face and has the mirror 23 placed against the other face, the mirror being either a dielectric reflector or a mosaic of metal reflectors. The mirror 23 is in contact with the face 11 of a cathode-ray tube 13, wires 33 being embedded in the face 11 so that a charge established by an electron beam 31 is conducted to a location adjacent the KDP layer where the charge is temporarily stored. The active element 5 is pumped by a source 39 which may be a helical flash tube, and the phase delay introduced by the retardation plate 26 on the emitted light passed by the polarizer 25 reduces the reflected light sufficiently to generally prevent lasing. However, at the location where the electron beam establishes a charge, the KDP layer 24 introduces a compensating phase change which cancels a sufficient amount of the phase delay introduced by the retardation plate to cause stimulated emission along a single axis 29. This axis, and hence the direction of the light beam, can be changed by moving the electron beam to another point 21 on the face 11. In a modification, Fig. 2 (not shown), the cavity mirrors 7<SP>1</SP>, 23<SP>1</SP> are both spherical and the laser active element 5<SP>1</SP> is of dumb-bell shape instead of spherical as in the previous embodiment. The reflector 23<SP>1</SP> forms the target of the cathode-ray tube, and is in direct contact with a spherically-shaped compensating element 24<SP>1</SP> having an SnO coating 25<SP>1</SP>, the sandwich assembly constituting the tube front. As KDP is uniaxial it cannot be used as a compensating element, and element 24<SP>1</SP> is composed of a crystalline material of cubic symmetry such as zinc sulphide (ZnS) or hexa-methylene tetramine (HMTA). In this arrangement the intensity of the simulated emission along the chosen axis 29 is determined by a modulator 41 connected between a D.C. source 34<SP>1</SP> and a control element 35<SP>1</SP> of the cathode-ray tube which controls the intensity of the electron beam. The KPD or other substance element 24 may exhibit either electrooptical or magneto-optical effects, the polarizer 27<SP>1</SP> may be omitted where the laser has inherent polarization properties, and the charge on face 11 may be removed rapidly by using a " flood gun." Reference has been directed by the Comptroller to Specification 985,204.