Abstract
An active beam-pointing stabilization system has been developed for a
high-power KrF laser system to eliminate the long-term drift of the
directional change of the beam in order to have a stable focusing to a
high intensity. The control of the beam direction was achieved by a
motor-driven mirror activated by an electric signal obtained by monitoring
the position of the focus of the output beam. Instead of large sized
UV-sensitive position sensitive detectors a simple arrangement with
scatter plates and photodiodes are used to measure the directionality of
the beam. After the beam stabilization the long-term residual deviation of
the laser shots is ~14 μrad, which is comparable to the shot-to-shot
variation of the beam (~12 μrad). This deviation is small enough to keep
the focal spot size in a micrometer range when tightly focusing the beam
using off-axis parabolic mirrors.
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