EXCIMER  LASERS

     Excimer lasers produce intense pulsed output in the ultraviolet. The excimer is unique because the lasing molecule is one consisting of a halogen and an inert gas. This molecule is transient and exists for only a moment in time. Like the nitrogen laser, a fast, high-current discharge is required to produce the excimer molecule, but excimers lasers are considerably more complex since they operate at high pressures and one of the active gases is highly toxic and corrosive. The first discharge excimer lasers were simply TEA CO₂ lasers (which, like nitrogen lasers, feature long transverse electrodes) with an excimer gas mix and UV optics. The problem with this scheme was the halogen gas in the excimer mix, which quickly attacks laser electrodes. Manufacturers quickly adapted their lasers to handle these halogens and excimer technology progressed especially in the electronics used to produce high-current pulses in the laser.

      Modern excimer lasers produce pulses with energy ranging from 0.1 to 1 J and can (for a large industrial laser) produce these pulses at a rate of over 300 per second. Pulses are fast, with a FWHM of 10 to 30 ns. Fast pulses combined with high peak powers (a 0.5-J pulse with a 20-ns width corresponds to a power of 25 MW) serve to ablate target material without heating the surrounding material, a desirable effect for many processing purposes.