A window laser having at least one window region with a transparent waveguide layer optically coupled to an active region generating lightwaves. The waveguide layer is characterized by a broader guided transverse mode for the lightwaves than the active region and may have a thickness which is greater than the active region, a refractive index difference with respect to cladding layers which is less than a refractive index difference between the active region and the cladding layers, or both. The waveguide layer may be coupled to the active region via a transition region characterized by a gradual change in the guide mode width of the lightwaves, such as from a tapered increase in thickness of the waveguide layer in a direction away from the active region. The preferred method of making window regions having these transparent waveguides is impurity induced disordering, in which the interfaces between active region and cladding layers is smeared to produce the waveguide layer with increased bandgap and a graded transverse refractive index profile. The laser is characterized by a high power output beam with reduced far field transverse divergence.