We have successfully used adaptive mirrors to compensate thermo-optical aberrations in solid state lasers. However, from these experiments we learned that commercially available deformable mirrors are not very suitable for this purpose. Either the spatial density of their actuators was not sufficient or their reflectivity was not high enough. The surfaces of many types of deformable mirrors are made from special materials that can not be coated with the large number of scatter-free dielectric layers that are required to achieve the highest reflectivity. These drawbacks prompted us to start our own mirror development. We developed so-called unimorph mirrors specifically for laser applications. The mirrors basically consist of a super-polished glass disk and a piezo-electric disk which are bonded together. The glass disk can be furnished with the very best coatings that can be produced today. These deformable mirrors can thus withstand many kW of continuous laser power.