Pre-ionizing electrode arrangement for a gas discharge laser

In a gas-discharge laser including an optical axis situated between a pair of main electrodes, said optical axis and said main electrodes being substantially parallel to each other, and wherein one of said pair of main electrodes is arranged to have a lower voltage than the other of said pair of main electrodes during operation of said laser, the improvement comprising a plurality of pre-ionizing electrode arrays arranged on two sides of said pair of main electrodes to provide ionization throughout the discharge volume between the main electrodes, said arrays including means for causing a sliding-spark discharge in said pairs of pre-ionizing electrodes, the sliding-spark progressing sequentially from a first pair to a last pair, wherein said pairs of pre-ionizing electrodes are symmetrically displaced on opposite sides of the optical axis and the main electrodes.