Dark line resonances, narrowed with a buffer gas to less than 100 Hz width,
are observed in a Cs vapor cell using a directly modulated vertical-cavity
surface-emitting laser (VCSEL). An external oscillator locked to one of th
ese resonances exhibits a short-term stability of sigma (y)(tau) = 9.3 x 10
-12/root tau, Which drops to 1.6 x 10(-12) at 100 s, A physics package for
a frequency-reference based on this design could be compact, low-power, and
simple to implement.