In electrical discharge apparatus, such as a gas laser, in which a glow discharge is to be produced in a gas between two electrodes, at least one pre-ionizing member is placed near the discharge space and extending between the electrodes so that current flows in the member which is made of intermediate resistivity material such as crystalline semiconductor material. As a result, the discharge space is pre-ionized which assists initiation of the main discharge. The pre-ionization may be due to the formation of numerous small arcs between the electrodes and the member and the resulting production of ultra-violet light.
The invention provides a gas-discharge laser comprising an array of pre-ionizing electrodes (PIP) operating by a sliding-spark discharge; there being an array provided on either side of each of the main electrodes (ME1, ME2) of the laser.
