GB1011439A - Improvements in or relating to electric discharge lamps - Google Patents

Abstract

1,011,439. Metal-vapour lamps. GENERAL ELECTRIC CO. July 1, 1964 [July 1, 1963], No. 27188/64. Heading H1D. An electric discharge lamp comprises a tubular elongated envelope of material resistant to the attack of potassium vapour, two electrodes sealed respectively into opposite ends of the envelope, and an ionizable medium within the envelope and comprising potassium and an inert starting gas, the quantity of the potassium being such that in use of the lamp the potassium vapour pressure lies in the range of 30 to 540 torr. The ceramic envelope 2 of the lamp shown is of sintered transparent polycrystalline alumina 8.5 cm. long, 6 mm. in internal diameter and having a wall thickness of 0.8 mm. increased to 1.4 mm. at the ends. Metal, preferably niobium, exhaust tubes 5 and 6 are welded to niobium end closures 3 and 4 sealed by a glassy mixture comprising mainly aluminium and calcium oxides into the envelope. Electrodes 7 and 8 each comprise tungsten coils coated with activating material slipped or screwed on to rods or studs of thoriated tungsten crimped or welded into the exhaust tubes, one, 5, of which may be a dummy while the other, 6, has a filling aperture 9 and a pinched off cold weld 10. The starting gas may be argon or preferably xenon. The projecting length of the tube 6 may be predetermined to provide a desired potassium saturation vapour pressure. The potassium may be introduced by heating to bursting point a glass ampoule located in an exhaust manifold connected to the envelope, or by electrolysing potassium into a glass appendix from a molten bath of a potassium salt. The lamp may be operated continuously on D.C. or A.C. or may be pulsed, and is suitable as a pump for a laser of neodymium barium crown glass. Drawings of the percentage absorption of a neodymium glass and of the emission spectrum of the lamp are provided (Figs. 2 and 3, not shown).