Amplification of xuv harmonic radiation in a gallium amplifier.

We report the observation of amplification of an xuv harmonic pulse in an xuv laser. The 21st harmonic of a frequency-doubled 1.3-psec neodymium chirped-pulse-amplification laser pulse was injected into the gain region of an 18-mm-long Ga XXII x-ray amplifier. A gain of approximately 3 was recorded for the 21st harmonic, relative to the unamplified 19th and 23rd harmonics when the harmonic wavelength was tuned to overlap the 25.11-nm {ital J}=2--1 laser transition.