  We devise a laser-controlled adaptive optical element which operates
intracavity under high intensity radiation. This element substitutes a
conventional mechanically deformable mirror and is free of critical
heat-sensitive components and electronics. The deformation mechanism is based
on the projection of a CW control laser onto a specially designed mirror.
Mounted to a water-cooled heat sink, the mirror can handle laser radiation
beyond 3 MW/cm^2. The properties of the adaptive optical element including the
maximum correctable wavefront pitch of 800 nm are discussed. The successful
implementation in a multipass thin disk amplifier is presented. An improvement
of the beam quality by a factor of three is achieved. We identify measures to
enhance the performance of the adaptive optic towards efficient operation in a
high-power laser system.
