Experimental study of a generalized self-filtering unstable resonator applied to an XeCl laser

A diffraction-limited laser beam of 3.5 mJ with a pulse width of 11 ns and a brightness of 4.8×10¹³ W-cm^-2-Sr ^-1 has been obtained by applying a generalized self-filtering unstable resonator (SFUR) scheme to a short-pulse XeCl laser. In accordance with the theory, the generalized SFUR maintains the excellent properties of the SFUR, such as high transverse-mode discrimination, fast establishment of steady-state condition, and diffraction-limited output beam, but offers the possibility of having high magnification and higher mode volumes with shorter resonator lengths. It is possible to demonstrate that with the generalized SFUR, one can increase, by a factor more than two, the mode volume with respect to the confocal case by leaving the cavity length unaltered. These properties make the nonfocal SFUR particularly suitable for short-pulse excimer lasers