A solid-state laser beam amplifier with integrated reflective surface. A rectangular slab gain medium receives a first portion of an input laser beam along a first zigzag reflection path within the slab. The gain medium also receives a second portion of the input laser beam that has been reflected from an integral reflective surface such that the two portions traverse the gain medium along complementary zigzag paths. The zigzag paths are defined by total internal reflection of the beam portions as they propagate through the gain medium slab. A similar reflective surface may be positioned relative to the exit end of the gain medium slab, which redirects all of the output beam portions in a parallel direction. The gain medium may be Ytterbium or neodymium doped yttrium aluminum garnet. The gain medium may be formed as a high aspect ratio rectangular slab and may be clad with sapphire. The reflective surfaces may function by total internal reflection or may employ a reflective material, such as a dielectric coating. A section of undoped medium may be applied to the entrance or exit end of the gain medium slab to control angles of incidence and refraction.