Self-filtering unstable resonator operation of XeCl excimer laser

A diffraction-limited laser beam with a pulse energy of 120 mJ and brightness up to a magnitude order of 10
¹⁴
W . cm
^-2
. Sr
^-1
has been achieved in an X-ray preionized discharge XeCl laser by using a self-filtering unstable resonator. The near- and far-field laser properties have been examined.