In an excimer laser, the laser medium is excited by means of a high-speed transverse electrical discharge. DC high voltage is supplied to a pulse-forming network that consists of a high-performance thyratron switch, a magnetic pulse compression system and banks of storage capacitors. These components generate a high-speed current pulse across the electrodes. As the current pulse traverses the electrode gap, the lasant gases are ionized and form the excimer molecule. The following graphic depicts the laser discharge process.
Due to the excimer constituent relaxation times, thermal effects influence discharge and particulate formation. Laser discharge can only occur at repetition rates of less than 1Hz unless the gas between the electrodes is constantly replaced with fresh gas. The gas reservoir function is to provide a large volume of lasing gas so that gas refreshment can occur. A high-speed blower fan recirculates the laser gas at speeds of 1 to 5 meters per second so that the volume of the gap is completely refreshed between pulses at repetition rates of up to 400Hz. After discharge, the spent gas mixture flows across heat exchangers, which remove the heat that was generated during the pulse. Most lasers employ some form of particle filtration to clean the gas mixture prior to its passing again across the electrodes. As the gas flows around in the recirculation loop, excited gas molecules return to normal sizes.