A metal vapor discharge lamp includes a cathode comprising a reservoir of liquid cesium. Metallic cesium which is eroded from the cathode surface by the action of the discharge is returned to the reservoir by the combined effects of gravity, evaporation, condensation, and diffusion to provide a highly stable, long-lived lamp.The intense infrared pulse output of cesium vapor discharge lamps of the present invention is well suited for triggering light-activated semiconductor switches through dielectric pipe networks and for pumping neodymium glass or neodymium-YAG lasers.