Patent ID: 8310673

Claim:
A light source which, when in use, is inserted into a reaction chamber for generating a plasma atmosphere, and which is employed for determining an atom or a molecule density of the plasma atmosphere through an absorption spectroscopy, said light source comprising: a tubular casing comprising a base portion and tip end; a cooling medium passage for causing a cooling medium to flow therethrough, the passage being provided along an inner wall of the casing and comprising a supply passage extending from the base portion to a bottom portion disposed near the tip end and a drain passage extending from the bottom portion to the base portion, the supply passage communicating with the drain passage at the bottom portion; a lens provided at the tip end of the casing; a first electrode and a second electrode which are provided in the casing and before the lens so as to be vertical to an axis of the casing and parallel to each other; an insulating spacer provided between the first electrode and the second electrode; a hole axially penetrating center portions of the first electrode, the insulating spacer, and the second electrode; and an electric discharge gas passage for introducing an electric discharge gas, along an inner wall of the cooling medium passage, to a back surface of the lens so that the electric discharge gas is reflected by the lens and flows through the hole in a direction of the base portion.