Data are presented of efficient single-pass green-light second-harmonic generation from a periodically-poled LiNbO₃ waveguide crystal. Over 220 mW maximum green light output power with an optical-to-optical conversion efficiency of over 70% is measured. Green-induced infrared absorption is indicated to be the major absorption loss in this waveguide. A simple analytic expression is derived and used to estimate the crystal waveguide absorption coefficient, which was found to be 7×10⁻³ cm⁻¹.