  We developed a high-power laser system at a wavelength of 399 nm for laser
cooling of ytterbium atoms with ultraviolet laser diodes. The system is
composed of an external cavity laser diode providing frequency stabilized
output at a power of 40 mW and another laser diode for amplifying the laser
power up to 220 mW by injection locking. The systematic method for optimization
of our injection locking can also be applied to high power light sources at any
other wavelengths. Our system, which does not depend on complex nonlinear
frequency-doubling, has great importance for implementing transportable optical
lattice clocks, and is also useful for investigations on condensed matter
physics or quantum information processing using cold atoms.
