LIGHT SOURCE

摘要

[PROBLEMS] To realize a light source enabling accurate measurement of the density of particles without disturbing conditions of plasma. [MEANS FOR SOLVING THE PROBLEMS] The light source has a tubular casing (12), a cooling medium channel (30) provided along the inner wall of the casing and allowing a cooling medium to flow in the channel, a lens (50) disposed at the front end of the casing, a first electrode (44) and a second electrode (45) disposed at positions located on this side of the lens and in the casing so as to be vertical to the axis of the casing and parallel with each other, and an insulation spacer (46) disposed between the first and second electrodes. A hole (47) axially extends through the centers of the first electrode, the insulation spacer, and the second electrode. The light source further has an electric discharge gas channel for introducing an electric discharge gas along the inner wall of the cooling medium channel toward the rear surface of the lens and causing the discharge gas to be reflected by the lens to allow the gas to flow through the hole.