  A thermal atomic ensemble-based laser source with superior frequency
stability is proposed that relies on the accumulated contributions from an
abundance of nonzero-transverse-velocity atomic ensembles. Compared with the
traditional case in which only atoms with near-zero transverse velocities are
utilized, the amplitude of the optical Ramsey fringes for a thermal calcium
beam can be dramatically enhanced by three orders of magnitude or more, thus,
the signal-to-noise ratio can be improved 33-fold. Based on the recent results
of atomic interferometry-based laser stabilization, a quantum projection
noise-limited frequency instability less than 2E-17/tau^0.5 is feasible. Such
an ultrastable laser has promising applications in diverse areas, including
metrology and astronomy.
