  Ultraviolet (UV) diode lasers are widely used in many photonics applications.
But their frequency stabilization schemes are not as mature as
frequency-doubling lasers, mainly due to some limitations in the UV spectral
region. Here we developed a high-performance UV frequency stabilization
technique implemented directly on UV diode lasers by combining the dichroic
atomic vapor laser lock and the resonant transfer cavity lock. As an example,
we demonstrate a stable locking with frequency standard deviations of
approximately 200 KHz and 300 KHz for 399nm and 370nm diode lasers in 20
minutes. We achieve a long-term frequency drift of no more than 1 MHz for the
target 370nm laser within an hour, which was further verified with fluorescence
counts rates of a single trapped $^{171}$Yb$^+$ ion. We also find strong linear
correlations between lock points and environmental factors such as temperature
and atmospheric pressure.
