Patent GB-1086319-A (GB)
Title: Lasers
Inventor: HARDY WILTON AUDUBON
IPC: H01S3/101
Filed: 1964-11-19
Abstract: 1,086,319. Lasers. INTERNATIONAL BUSINESS MACHINES CORPORATION. Nov. 19, 1964 [Dec. 31, 1963], No. 47060/64. Addition to 1,055,840. Heading H1C. [Also in Division G2] The optical resonator of a laser contains a focusing element and an arrangement for masking a portion of one reflecting surface. In Fig. 1 the active medium consists of a heliumneon gas element 2 which is pumped by a source 4 and is located between concave mirrors 6, 8, a lens 14 being provided so that an image P on one mirror is focused at Q on the other mirror. In Fig. 2 (not shown) a further concave mirror 18 is used as a focusing element instead of a lens. An apertured mask 16 is placed against mirror 6 so that reflectivity is destroyed except at the positions of the apertures. One of the mirrors is partially transmitting and the emergent light beam is of a form determined by the apertures. Various shapes of apertures in the form of geometric configurations or characters may be used, Figs. 3a to 3c (not shown). Various image patterns are produced in the arrangement in Fig. 4 (not shown), in which the mask is replaced by rods 20 inserted through mirror 6, a movable metal leaf 22 being associated with each rod. When a potential is applied to a rod, the associated leaf 22 is deflected in the manner of the leaves of a gold-leaf electroscope and reflectivity is spoilt at the adjacent surface of mirror 6. By selectively applying potentials to the various rods various patterns of radiation are focused on mirror 8. An alternative method of producing electrically-determined patterns is by the use of a raster of electro-optical light modulators 36, Fig. 6 (not shown), in association with polarized light emitted from a helium-neon active element with a window 30, Fig. 5 (not shown), set at the Brewster angle. The light modulators 36 can be so positioned that laser oscillation over the regions associated with respective modulators is either suppressed or permitted when the modulators are energized by electric potential. By selectively applying the potential to various modulators the image reflectivity of mirror 6 is controlled. The modulators each consist of a flat polished plate of ammonium dihydrogen phosphate (ADP) or potassium dihydrogen phosphate (KDP) having thin metallic electrodes 38, 40 to which beds 42, 44 are attached, Fig. 5a (not shown). A microscope is shown in Fig. 8 in which a concave mirror 54 serving as a support for an object 56 to be examined is adjacent a transparent curved surface 63 of a ruby or neodymium-doped glass active medium 50. The opposite curved surface 64 of the medium forms a partially reflecting concave mirror. The active medium is pumped by a lamp 52 located within a reflector 51. The reflecting surfaces 54, 64 are confocally disposed and cause a conjugate image of the object to appear at position 66. The image and object appear as two magnified images 58 on a screen 65 after passing through a magnifying lens 60 and a filter 62 for removing light from the lamp 52 but passing the laser radiation. Conventional optical microscopes can be used for further magnification. Reference has been directed by the Comptroller to Specification 985,204.