Patent GB-957235-A (GB)
Title: Optical radar system
IPC: H01S3/042
Filed: 1962-03-15
Abstract: 957,235. Lasers. HUGHES AIRCRAFT CO. March 15, 1962 [April 13, 1961], No. 9988/62. Headings H3B and H4D. An optical radar system includes a laser. Solid state lasers.-A laser comprises a cylindrical rod of pink ruby (Al 2 O 3  doped with Cr 2 O 3 ) and a source of pumping light so arranged that substantially all the light impinges on the ruby rod. In Fig. 3, a ruby rod 30 containing less than 0.1% by weight of chromium is disposed coaxially within a helical flash-tube 28. A cylindrical reflector 38 directs the light on to the ruby. The ends 26, 30 of the ruby rod are silvered to provide at least 10% reflection and to define a regenerative path. One end 32 has a portion not silvered to allow a free passage for the output beam 34 which is monochromatic and coherent. In Fig. 4 a flashing gas 52 is disposed between a ruby rod 40 and a reflecting cylinder 50. Electrodes 54, 56 are energized to cause emission of pumping light by the gas. The stimulated output beam emerges through an opening 46 in the reflective coating 44. In Fig. 5, a rod 60 is disposed within a hollow flash tube 62. Fluorescein 64 fills the space between the rod and the flash tube and converts the light from the flash tube into predominantly green light suitable for pumping the ruby. In Fig. 7, a cylindrical flash tube 72 is disposed within a hollow cylinder 70 of laser material. The cylinder 70 is surrounded by a cylinder 74 filled with cooling material 76. A laser element may be coated with material which is transparent to the pumping energy but absorbent at the laser output frequency. Alternatively, the element may be enclosed and cooled with a material such as di-iodomethane which has a high refractive index 1.75 (ruby 1.76) so that in effect there is no internal reflection. In Fig. 12, the regenerative path for the laser output is defined by four prisms 138, 140, 142, 144 and a Fabry-Perot interferometer 148 all outside the element. The regenerative path of an element 160, Fig. 13, may be defined by reflective plates 162, 164 displaced from the non-reflective ends of the element. Parabolic or elliptical mirrors may be used to concentrate the light from a pumping source 184 on to a laser element 182, Figs. 15, 16. Refrigerated operation, Fig. 8.-A rod 78 of laser material is mounted on a rod 88 of copper or sapphire. The major portion of the rod 88 is immersed in liquid nitrogen 90 in a Dewer flash 92. A hollow cylindrical flash tube 94 surrounding the flash tube is cooled by liquid in a jacket 100. Optical radar system, Fig. 17.-A power supply 206 pulses a gas filled flash tube 204 when triggered by a synchronizer 208 which simultaneously starts a scanning operation in oscillographs 214, 216. A laser rod 202 associated with the flash tube transmits a beam of monochromatic coherent light towards a target 212. The reflected light is filtered at 230 and is focused on a photo-electric cell 226 by a parabolic reflector 224. The reflected pulse of light is indicated on an oscillograph 216. The transmitted pulse is detected by a photo-cell 218 and is indicated by a second oscillograph 214.