Summary form only given.We consider coherent dark resonances in Cs vapor cells where the effective interaction time between atoms and light is increased through the addition of a buffer gas or through a coating of the cell walls with siloxane. The light sources are two diode lasers phase locked at 9.2 GHz frequency difference, corresponding to the hyperfine splitting of cesium. The phase-locked loop eliminates difference frequency jitter and leads to resonances narrower than 50 Hz, which can be applied to various precision experiments.
When neon is introduced as a buffer gas the interaction time of cesium atoms in a vapor cell with resonant laser beams is drastically increased. Using a pair of phase-locked lasers we have observed linewidths as narrow as $42 $Hz for coherent dark resonances in a cesium vapor cell. We study the influence of power and pressure broadening and systematic shifts of the resonance frequency. Our experiments demonstrate that coherent dark resonances could rival direct radio-frequency precision measurements, which have a wide range of applications in physics.
We report the results of experimental investigation of the Raman – Ramsey method of pulsed excitation of coherent population trapping (CPT) resonances in a rubidium vapour cell filled with a mixture of Ar and Ne buffer gases. For the development of compact quantum microwave frequency standards, this method is an alternative to the pulsed optical pumping method recently implemented using the same rubidium cell. Both methods have advantages over the traditional double radio-optical resonance technique, the main of which is the substantial suppression of the light shift of the clock transition frequency, since the evolution of the coherence of atomic states forming the clock transition occurs in the absence of laser radiation in the cell. The narrow (110 – 240 Hz) Raman – Ramsey resonances are obtained using the scheme of pulsed excitation of CPT resonances on the D 1 lines of the 87 Rb atom with the same linear (lin||lin) polarisations of the bichromatic laser radiation components. The process of optimising the central fringe linewidth, its contrast, and the linewidth-to-contrast ratio is described. The magnetic dependence of the Raman – Ramsey line central fringe linewidth is experimentally investigated.
The hyperfine relaxation of a population difference, produced by optical pumping, between the
F=1 mF=0 and
F=2 mF=0 energy levels of the ground state of
Rb87, has been studied in cells containing neon, argon, helium, or krypton as a buffer gas. The relaxation times
T1 and
T2 have been measured as a function of the rubidium vapor pressure in the cell. The relaxation rate due to spin exchange in
Rb87-
Rb87 collisions has been found equal to 65 ${\mathrm{sec}}^{\ensuremath{-}1}$ at 44\ifmmode^\circ\else\textdegree\fi{}C, and the diffusion coefficients of
Rb87 atoms in He, Ne, and Ar evaluated as 0.6, 0.31, and 0.22
cm2 ${\mathrm{sec}}^{\ensuremath{-}1}$, respectively. The cross section for
Rb87-Ne and
Rb87-Ar collisions are found to be 1.6\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}22}$
cm2 and 9\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}22}$
cm2. These values are in general agreement with values previously obtained by other methods. The extrapolated values of
T21 for zero vapor pressure of rubidium are 185, 237, and 318 ${\mathrm{sec}}^{\ensuremath{-}1}$ for Ne, He, or Ar, respectively. Relaxations by the pumping light or by the magnetic field inhomogeneities are also discussed.
It was shown by Kocharovskaya and Khanin [Sov. Phys. JETP 63, 945 (1986)] that a comb of optical pulses can induce a ground-state atomic coherence and change the optical response of an atomic medium. In our experiment, we studied the propagation of a comb of optical pulses produced by a mode-locked diode laser in rubidium atomic vapor. Electromagnetically induced transparency (EIT) was observed when the pulse repetition rate is a subharmonic of the hyperfine splitting of the ground state. The width of the EIT resonance is determined by the relaxation rate of the ground-state coherence. Possible applications to magnetometery, atomic clocks, and frequency chains are discussed.