A tunable blue light source with narrow linewidth for cold atom experiments

We present a 397-nm frequency-doubling system with a quasi-phase-matched KTP crystal (PPKTP) which features tunable, narrow linewidth, high power, and excellent mechanical stability. Using 20-mm and 30-mm-long PPKTP crystals, we establish two experimental setups based on different external cavity parameters. By testing the beat signal of these two lasers, the linewidth for the system is measured to be less than 2.5 MHz. The maximum power of blue light can be achieved up to 40 mW. With these performance characteristics, the constructed blue laser system is useful for applications in cold atom physics and precision measurements.