We describe a diode-laser-based system capable of generating >50 mW of single-frequency radiation near 425 nm. An alternative extended cavity diode laser injection seeds a semiconductor amplifier, whose output is frequency doubled by a nonlinear crystal placed in a power enhancement cavity. This system is particularly well suited for high-resolution spectroscopy in the blue region, and for laser cooling and trapping of calcium atoms. (C) 2004 Society of Photo-Optical Instrumentation Engineers.43613111313