  Large scale laser interferometric gravitational wave detectors (GWDs), such
as GEO 600 require high quality optics to reach their design sensitivity. The
inevitable surface imperfections, inhomogeneities and light-absorption induced
thermal lensing in the optics can convert laser light from the fundamental mode
to unwanted higher order modes, and pose challenges to the operation and
sensitivity of the GWDs. Here we demonstrate the practical implementation of a
thermal projection system which reduces those unwanted effects via targeted
spatial heating of the optics. The thermal projector consists of 108
individually addressable heating elements which are imaged onto the beam
splitter of GEO 600. We describe the optimization of the spatial heating
profile and obtained results.
