  We use the technique of coherent population trapping (CPT) to access the
ground hyperfine interval (clock transition) in $^{133}$Cs. The probe and
control beams required for CPT are obtained from a single compact diode laser
system. The phase coherence between the beams, whose frequency difference is
the clock frequency, is obtained by frequency modulating the laser with an
electro-optic modulator (EOM). The EOM is fiber coupled and hence does not
require alignment, and the atoms are contained in a vapor cell. Both of these
should prove advantageous for potential use as atomic clocks in satellites.
