  We demonstrate a compact and robust device for simultaneous absolute
frequency stabilization of three diode lasers whose carrier frequencies can be
chosen freely relative to the reference. A rigid ULE multi-cavity block is
employed, and, for each laser, the sideband locking technique is applied.
Useful features of the system are a negligible lock error, computer control of
frequency offset, wide range of frequency offset, simple construction, and
robust operation. One concrete application is as a stabilization unit for the
cooling and trapping lasers of a neutral atom lattice clock. The device
significantly supports and improves the operation of the clock. The laser with
the most stringent requirements imposed by this application is stabilized to a
linewidth of 70 Hz, and a residual frequency drift less than 0.5 Hz/s. The
carrier optical frequency can be tuned over 350 MHz while in lock.
