BEAM DIVERGENCE STUDIES ON HARD EDGE UNSTABLE RESONATORS FOR A LONG-PULSE XECL EXCIMER-LASER

The focusability of a long pulse XeCl excimer laser has been improved using confocal positive branch unstable resonators where the outcoupli ng is done through the convex mirror. A nearly diffraction limited out put beam is obtained from hard edge unstable resonators. An improvemen t of the far field energy distribution is achieved with partial reflec ting hard edge outcoupling mirrors. The phase delay between the centra l part of the beam and the beam edge caused by these partial reflectin g mirrors can be reduced by using phase unifying mirrors. Using unstab le resonators a brightness of 1.4 x 10(15) W/cm(2) sr has been obtaine d from a long pulse XeCl excimer laser (C) 1997 Elsevier Science B.V.