Femtosecond-pulse-driven 10-Hz 41.8-nm laser in Xe ix

We report the observation of extreme UV lasing at 41.81 nm on the 4d95d1S0−4d95p1P1 transition in Xe ix, as proposed by Lemoff [ Opt. Lett.19, 569 ( 1994)]. A 10-Hz circularly polarized 800-nm laser pulse with an energy of ∼70 mJ and a duration of ∼40 fs is longitudinally focused to a peak intensity of >3 × 1016 W/cm2 over a length of 8.4 nm in a differentially pumped cell containing 12 Torr of Xe gas. Laser amplification was observed with an estimated gain coefficient of 13 cm−1 and a total gain of exp(11).