We demonstrate a novel method for improvement of spatial beam quality by use of the angular selectivity of a thick phase grating inserted into various laser cavities. Preliminary experiments with an intentionally degraded beam from a Nd:YVO4 laser have enhanced beam propagation factor M2 by a factor of 4.5. Operation with a broad-area laser diode in an external cavity with a thick grating was achieved. We obtained 100 mW of cw power in a beam with an M2 of 1.3. Moreover, a reduction of the output spectrum by as much as a factor of 3.8 was obtained