Performance characteristics of an electron beam pumped XeF(C→A) laser with positive branch injection-controlled unstable resonators

The performance of injection controlled on-axis (centrally obstructed) and off-axis (non centrally obstructed) unstable resonators with magnifications between 2 and 3 for an electron beam pumped high power XeF(C→A) excimer laser system has been evaluated both in the near and far field. The angular beam divergence with the tested resonators was typically 2-3 times that of a diffraction-limited beam. A beam divergence angle as low as 128 µrad was obtained with a circular cross-section on-axis unstable resonator geometry of magnification 3. A peak brightness of 3×10 14 W/(sr·cm 2 ) with a beam divergence of 160 µrad was measured for a square cross-section off-axis resonator of magnification 2. In comparison with an on-axis resonator of the same magnification, the experimental results demonstrated that an off-axis unstable resonator offers an effective configuration for improving the laser beam quality without decreasing the output energy of an injection controlled XeF(C→A) excimer laser.