Over millions of laser pulses, repeated discharges across the electrodes induce the preionization pins and electrodes to sputter. The plastic insulation materials within the discharge chamber degrade under the intense UV exposure that occurs during lasing. These by-products react with the halogen gas in the laser mixture causing the formation of UV absorbing impurities. The halogen concentration is depleted by these reactions. The combination of halogen depletion and impurities formation causes the laser light output to decrease over time when constant high voltage is applied to the discharge circuit. To maintain constant light output, the high voltage must be adjusted to compensate for lasing efficiency loss. Modern excimer lasers use laser energy monitoring devices to measure beam output and computer controls to make automatic high voltage adjustments.
Halogen depletion effect