To generate a homogenous plasma discharge, an initial electron density of 107 to 108 cm-3 is required. Typical industrial excimer lasers use spark preionization to achieve this initial density. When the spark pins fire during the initial phase of the high-voltage current pulse, the UV light produced ionizes the gas mixture, inducing a large area plasma discharge in which the excited species are efficiently created.
1. Preionization
The main gas discharge is carried through the laser gas neon buffer gas constituent. Discharge current densities approach 10 A/cm2. Kr+ and F- ions, as well as other excited species, are formed during the discharge.
2. Main gas discharge
The main discharge forms a large, highly-unstable population of excited KrF molecules, which have a lifetime of about 2.5ns.
3. Excited dimer formation
During and after the discharge, the excited dimmers, which are formed immediately, begin to transition to the unbound lower state, producing photon emissions at 248nm. This light is fed back through the discharge cavity by resonator optics at either end of the chamber. The remaining KrF molecules population is stimulated to transition by this feedback, thereby producing the UV laser light pulse. After the pulse completes, the gas constituents require a relaxation time of greater than 100ms before they can participate in the discharge again.
4. Laser transition yielding UV photons
