We report the demonstration of a near-diffraction-limited, compact, diode-end-pumped double-clad planar waveguide Nd:YAG laser. Efficient laser operation was achieved for the three dominant Nd 31 transitions, at 1.064, 0.946, and 1.32 mm, with TE polarized output powers of 1.33, 0.57, and 0.33 W for the available output couplers. The output beam from the monolithic plane -plane laser cavity had measured M 2 values of 1.0 and 1.8 perpendicular and parallel, respectively, to the plane of the waveguide. © 2001 Optical Society of America OCIS codes: 140.3460, 140.3480, 130.2790. Planar waveguides are well suited to acting as host structures for diode-pumped solid-state lasers because of a combination of features related to their slablike geometry. The use of a planar end-pumped gain region avoids the need to use beam shapers or brightnessreducing f iber coupling to shape the normally asymmetric diode pump beam. The slab shape also offers good thermal management and consequent prospects for power scaling. These attractive features have been studied in recent research on bulk lasers 1 -3 and can be taken to their extreme in the case of a planar waveguide, for which, if the numerical aperture of the waveguide is high enough, the diode can simply be proximity coupled. 4 This pumping scheme lends itself to side pumping with diode bars of several tens of watts' output power, and recent results have demonstrated .12 W of continuous-wave and .8 W of passively Q-switched waveguide laser output. The output beam of the side-pumped waveguide laser is diffraction limited on the fast divergence axis owing to the use of a double-clad waveguide 4 ; however, for a plane-plane monolithic laser resonator the slow axis is highly multimode. In this Letter we describe end pumping of similar double-clad waveguides by a 4-W broad-stripe diode, leading to near-diffraction-limited output in both dimensions at output powers greater than 1 W. The prospects for scaling to higher powers are also discussed.The Nd:YAG waveguide used in this experiment is the same as that described in Ref. 4 and is shown schematically in Fig. 1. The f ive-layer double-clad structure was fabricated by Onyx Optics, Inc., by the direct-bonding method. The waveguide structure consists of a weak inner guide formed by a 20-mm-thick neodymium-doped YAG core (1 at. % Nd) sandwiched between two 5-mm-thick undoped YAG layers, which compose the inner cladding. Two 4-mm-thick sapphire layers form the outer cladding and provide excellent thermal conduction away from the doped core. The neodymium doping in the core provides a refractive-index increase, Dn ഠ 0.0004, with respect to the undoped cladding, leading to a numerical aperture (NA) of ഠ0.04. A greater refractive-index difference is present between the sapphire and the YAG, Dn ഠ 0.06, giving a NA of ഠ0.46. Because of the desire of keep the pump absorption length small, the doped core-to-undoped inner cladding ratio is relatively large compared with those of standard optical fiber designs. Thus the core is not optically...