Detection of ultra-high resonance contrast in vapor cell atomic clocks

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.