Pressure and Gap Length Dependence of Gap Breakdown Voltage and Discharge Current of Discharge-Pumped KrF Excimer Laser

Abstract

On an UV-preionized discharge-pumped KrF excimer laser with a charge transfer system, the electrical characteristics are discussed under the conditions of ambient pressure of 1.5 to 3.0 atm and discharge gap length of 14 to 21 mm for 20 to 34 kV of charging voltage of a primary capacitor bank at an optimum gas mixture of Kr/F₂/He/Ne=2.0/0.25/14.45/83.3% for a maximum laser output energy. A similarity relationship of gas breakdown voltage V_b and discharge current I_d, which are decisive factors for the laser characteristic, are found as a function of the product of gap length d and ambient pressure p. The gap breakdown voltage can be predicted by using a constant value of 20 as the product of the effective ionization coefficient and the gap length. Adapting the above similarity relationships of I_d=f(pd) and V_b=g(pd) to a normalized voltage-current characteristic studied previously, an actual voltage-current characteristic under any electrical condition can be estimated.