Quantitative comparison of different preionization schemes of KrF laser discharges

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fluorescence radiation from the ion–ion recombination process in the gas volume during the preionization phase, therefore allowing spatial resolution by partial imaging of the volume. Volume-integrated and temporally resolved measurements are carried out to determine the average of absolute preionization densities by comparison with a theoretical model of the temporal behaviour of the recombination process. Spatially resolved measurements reveal the distribution of the preionization density. The preionization densities determined from spark and sliding/corona discharges schemes are considerably higher (n_e ⁰?10¹² cm^-3) than those obtained from pulsed X-ray preionization (n_e ⁰?10⁷ cm^-3).