  We propose and demonstrate a novel detection scheme of clock signals and
obtain an ultra-high resonance contrast above 90%. The precision of the
signal's detection and the signal-to-noise ratio (SNR) of atomic clock signal
is improved remarkably. The frequency stability in terms of Allan deviation has
been improved by an order for the new detection under the equivalent
conditions. We also investigate density effect which produces the splitting of
the transmission peak and consequently a narrower linewidth of Ramsey fringes.
