Abstract: An excimer laser including a discharge chamber containing a mixture of halogen, rare gas and buffer gas uses two gas sources to replenish the halogen in the discharge chamber while maintaining the concentrations of all the gases at the optimum levels. One of the gas sources, source A, contains a mixture of the rare gas and the buffer gas in optimum concentrations. The other gas source, source B, contains both the rare gas and the buffer gas, in optimum relative concentrations, and also the halogen, in a concentration which is greater than optimum. As the laser operates and the gain of the laser decreases due to halogen depletion, gas from source B is injected into the discharge chamber to raise the halogen concentration. Gas is then released from the chamber to reduce the chamber pressure to the original level.

Abstract: A laser unit, including an optical power measuring device, measures, as the beam sample, a portion of the laser beam that is reflected out of the laser beam path by a wedge shaped front mirror, that is, an optical wedge. The front mirror has two surfaces, a partially reflective surface which reflects a portion of the beam back into the laser cavity and a nominally non-reflecting surface which permits a portion of the beam to exit the laser. The non-reflecting surface does in fact reflect some energy and, because of the wedge shape of the mirror, this energy is directed away from the laser beam path. The intensity of this off-path reflection is measured to determine the laser output power.