Slab lasers and method for producing high power coherent laser radiation of good quality. In one embodiment, a slab laser comprises a slab laser medium, an energy source configured to deliver energy to the laser medium, and first and second optical elements. The first optical element has a first reflective surface at a first boundary of the laser medium, and the second optical element has a second reflective surface at a second boundary of the laser medium. The first and second reflective surfaces face each other across the length of the laser medium, and at least one of the first and second optical elements includes a plurality of reflective regions configured to modify the phase distribution of the incident laser radiation propagating from the reflective regions. The first and second reflective surfaces are also positioned at an angle relative to each other to form a laser resonator.