This paper describes the development of a nanosecond oscillator-four pass a
mplifier XeCl laser system. A two times increase of the pulse peak power of
the free running amplifier module has been experimentally demonstrated. Th
e comparison with numerical results issued from a code describing the ampli
fication of the oscillator beam in the active amplifier medium suggests fur
ther experimental improvements to optimize the energy extraction from the a
mplifier. (C) 2001 Elsevier Science B.V. All rights reserved.