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 provides a large volume of lasing gas so that the constant gas refreshment can occur.
Excimer laser head cross section
A high-speed blower fan circulates 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 40Hz. After discharge, the spent gas mixture flows across heat exchangers that remove the heat generated during the pulse. Most lasers use 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.