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The appearance of the population difference in the ground state of the -system due to the spontaneous decay of the upper level into lower ones is considered. The resulting asymmetry of the coherent population trapping resonance is shown to lead to a frequency shift of the quadrature signal, which nonlinearly depends on the optical field intensity. In this case, this contribution is not suppressed due to the use of high modulation frequencies compared to the relaxation rate of ground state polarization (analogue of the Pound–Drever–Hall technique). A significant smallness of this shift when using a binary mixture of noble buffer gases is discussed. [ABSTRACT FROM AUTHOR]

Molecular nitrogen is often used as a buffer gas in cells with alkali metals due to its known ability to quench resonant fluorescence. It is widely believed that the suppression of spontaneous emission decreases the width of coherent population trapping resonance. However, our recent results have not confirmed this positive action of molecular nitrogen within the typical range of 87Rb concentrations and buffer gas pressures. On the opposite, we have observed the negative influence of quenching, the decrease in contrast of the coherent population trapping resonance in – configuration. In this work, we further confirm these results implementing the Ramsey spectroscopy, and compare the characteristics of the central fringe in nitrogen and neon, and show that the latter provides a significantly better contrast-to-width ratio. [ABSTRACT FROM AUTHOR]

We propose and demonstrate a simple technique for identifying the central Ramsey fringe of pulsed coherent population trapping resonance. An auxiliary optical field is applied during the free evolution time. It suppresses the nearby fringes but does not change the amplitude of central fringe practically, which marks it out clearly. The theory based on the density matrix equations for the Λ -system configuration of levels and Ramsey interrogation that takes into account the auxiliary optical field is presented and compared to the experiment with 87 Rb atoms. We also propose a technique for improving the middle- and long-term stability of compact atomic clocks. [ABSTRACT FROM AUTHOR]

The measurements of the metrological characteristics (amplitude, width, and shift in the magnetic field) of the dark pseudoresonance, which was proposed by Kazakov etal. [quant-ph/0506167] as the reference resonance for an atomic frequency standard, are reported. It has been shown that the characteristics of the pseudoresonance are worse than those of the unsplit electromagnetically induced transparency resonance for the excitation scheme with the lin || lin polarization on the D1 line of the 87Rb atom. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]

We propose and study, theoretically and experimentally, a new scheme of excitation of a coherent population trapping resonance for the D1 line of alkali atoms with nuclear spin I = 3/2 by bichromatic linearly polarized light (lin||lin field) under the conditions of spectral resolution of the excited state. The unique properties of this scheme result in a high contrast of dark resonance for the D1 line of 87Rb. © 2005 Pleiades Publishing, Inc. [ABSTRACT FROM AUTHOR]