Abstract: A preionization means for a gas-discharge laser, such as an excimer laser, comprises a stirrup member 26 and a preionization strip 20 secured thereto. To obtain the longest possible life of the laser with economical material use the preionization strip 20 is made from a different material from the stirrup member 26.

Abstract: For stabilizing the frequency of a narrow-band Excimer laser beam the interference rings of a Fabry-Perot interferometer 16 are projected onto a solid-state image sensor 18 and by means of the solid-state image sensor an electrical signal is generated which is dependent on the frequency of the laser beam. The electrical signal is compared with a stored reference signal to derive an adjusting signal 32 for an optical reflection grating 38 with which the frequency of the laser beam 12 is regulated to a desired value. The absolute value of the frequency of the laser beam 12 is determined by means of the optogalvanic effect.