Narrow linewidth gain measurements in KrF and ArF excimer amplifiers pumped longitudinally by high-power electrons

Abstract

Single-pulse KrF and ArF gain measurements have been conducted with an excimer amplifier longitudinally pumped by a high-power (∼5-MW/cm3 deposition) electron beam. This amplifier has preserved the narrow linewidth (∼10 GHz) exhibited by the probe laser beam generated by a grating-tuned, discharge pumped excimer laser. Single-pass gain was measured at 248.45 nm, the peak of the KrF laser gain profile, for a laser pulse with full width half maximum (FWHM) of 20 ns. Analysis of the gain data by a modified Rigrod steady-state formulation yielded values for the small-signal gain, the nonsaturable absorption, and saturation intensity of g0 = 12.6%/cm, α∼0.45%/cm, and Is = 4.1 MW/cm2, respectively, for a 750-Torr laser mix. The corresponding gain peak measurement for an ArF beam at 193.31 nm with FWHM of 15 ns produced g0 = 12.1%/cm, α∼0.70%/cm, and Is = 6.7 MW/cm2 for a 963-Torr laser mix with the same stopping power as the KrF mix. Measurement of gain at 193.68 nm, well away from gain peak, resulted in g0= 10.8%/cm, α∼0.70%/cm, and Is = 7.9 MW/cm2 for the same ArF mixture. Several amplified spontaneous emission and oscillator measurements have also been performed. Indications of laser gain saturation at high-power electron-beam deposition have been deduced.