Patent GB-1111631-A (GB)
Title: Improvements in or relating to apparatus for producing electromagnetic radiation
Inventor: MASTRUP FRITHJOF N
IPC: H01S3/093
Filed: 1965-04-26
Abstract: 1,111,631. Discharge lamps; lasers. T.R.W. Inc. 26 April, 1965, No. 17550/65. Headings H1C and H1D. A gas discharge device for pumping a laser rod 118 includes annular electrodes 110, 114 and coaxial hollow cylindrical insulating members 106, 108 defining an annular discharge passageway 112 between the electrodes and formed of a material transparent to radiation, a first current return conductor 100 positioned outside insulating member 106 and a second current return conductor 122 positioned inside insulating member 108, said conductors 100, 122 being connected together and to electrode 114 at one end thereof. In the arrangement shown a plurality of metal strips 122 are joined together at one end by a copper flange member 128 bolted to end-plate 102 and are held at the other end by a removable clamp 127. Electrode 114 is brazed to end-plate 102 which is bolted to return conductor 100. The centre conductor 168 of a coaxial cable 166 is connected to anode electrode 110 and the outer braid is connected to end-plate 104. The device is evacuated through connectors 134, 136. Insulating member 106 is formed of an arc-responsive gas-evolving material, e.g. " Plexiglass " (Registered Trade Mark). Electrodes 110 and 114 may be of stainless steel or tungsten. Application of a high-voltage pulse to the electrodes initiates a sliding spark along the surface of member 106 which is heated and evolves gas to sustain an arc discharge. The arc plasma is stabilized by the magnetic fields established by the currents through the plasma and the return conductors. Plenum chambers 130 and 132 receive discharge products from passageway 112. Cooling is provided by circulation of a cryogenic fluid, e.g. liquid nitrogen, through tubes 142, 144. In addition, end plates 102, 104 may be provided with cryogenically cooled baffle plates. Member 100 may have a reflecting inner surface or member 108 may be of laminar construction with a mirror surface adjacent an innermost gasevolving layer. An alternative method of arcinitiation comprises introducing a small quantity of a rare gas, e.g. xenon, into passageway 112 simultaneously with application of the voltage pulse. Lasers.-The laser active medium 118 is in the form of a longitudinally slotted rod, Fig. 2, and is located axially of the gas discharge passageway, the member 108 transparent to optical radiation and made of quartz, heat resisting glass or heavily-doped poor quality ruby providing a heat shield by rejecting ultra-violet radiation from the gas discharge. Strips 122 of copper, silver or aluminium are embedded in the slotted active medium and serve to convey heat from the active medium to end-plate 102 acting as a heat sink. Additional cooling of the active medium is provided by the coolant passing through helical tube 142. The laser active medium may consist of chromium-doped aluminium oxide, trivalent neodymium-doped calcium tungstate or neodymium or gadoliniumdoped glass. The passage of current through the embedded conductors 122 is stated to provide an electromagnetic screen for fields from the arc discharge which would otherwise cause Zeeman line splitting. The arrangement may operate as an optical amplifier or as a generator by providing external reflectors. A pulse generating circuit for exciting the pumping source is described (Fig. 4, not shown) which comprises a ladder arrangement of series-tuned circuits each having a different resonant frequency.