  Two cw single-mode violet (397nm) diode lasers are locked to a single
external-cavity master diode laser by optical injection locking. A double-pass
1.6GHz acousto-optic modulator is used to provide a 3.2GHz offset frequency
between the two slave lasers. We achieve up to 20mW usable output in each slave
beam, with as little as 25 \mu W of injection power at room temperature. An
optical heterodyne measurement of the beat note between the two slave beams
gives a linewidth of <=10Hz at 3.2GHz. We also estimate the free-running
linewidth of the master laser to be approximately 3MHz, by optical heterodyning
with a similar device.
