Pulsed ac Stark shifts monitored by Raman Ramsey fringes in sodium vapor.

We have employed Raman Ramsey fringes (RRFs) in sodium vapor to measure ac Stark shifts of the hyperfine levels by an off-resonant shift laser pulse. The ac Stark shifts are directly monitored by the RRF peak shifts and are proportional to the power and the pulse width and antiproportional to the detuning frequency of the shift laser. These findings endorse RRFs to be a strong tool for monitoring small pulsed perturbations.

Ultraslow matched-pulse propagation in sodium vapor.

We have observed ultraslow propagation of matched pulses in a parametric amplifying hot sodium vapor. A fractional delay of more than 1 and a gain of 28 have been simultaneously achieved for a probe pulse of width 100 ns, accompanying a conjugate Stokes pulse with similar gain and delay under a strong coupling beam. The results are compared with the preceding work by Boyer et al. [Phys. Rev. Lett. 99, 143601 (2007)].

Parametric oscillation in sodium vapor by using an external cavity.

We report on parametric oscillation in sodium atomic vapor by using an external cavity. Output powers of approximately 56 mW are obtained for both the signal and idler waves with the input coupling power of 290 mW, resulting in a conversion efficiency of 39%. The signal and idler frequencies are either upshifted or downshifted from the coupling frequency by the amount of the Na hyperfine splitting frequency, and the two waves are found to be strongly temporally correlated.

Four-wave parametric oscillation in sodium vapor by electromagnetically induced diffraction.

We have observed a novel type of parametric oscillation in sodium atomic vapor where four off-axis signal waves simultaneously build up under resonant and counterpropagating pump beams with elliptical beam profiles. The four waves, two of them Stokes shifted and the other two anti-Stokes shifted, have similar output powers of up to 10 mW with a conversion efficiency of 30% and are parametrically coupled by electromagnetically induced diffraction.

Electromagnetically induced diffraction in sodium vapor.

By using a sodium atomic vapor we have observed a honeycomb-type multiple-diffraction pattern that was due to a grating induced optically by three noncollinear bichromatic excitation beams. In particular, when the two incident frequencies satisfy the two-photon resonance condition and the atomic density is high, the diffraction is enhanced by electromagnetically induced transparency, and strong Stokes and anti-Stokes components are generated in well-defined directions.

Subkilohertz linewidths measured by heterodyne-detected coherent population trapping in sodium vapor.

Subkilohertz spectroscopy by coherent population trapping (CPT) has been performed in Na atomic vapor. The system employs a frequency-swept acousto-optic modulator for bichromatic excitation as well as a heterodyne-lock-in detection technique that permits the direct measurement of the CPT dispersion curves at a good signal-to-noise ratio. A CPT linewidth of -400 Hz was measured as well as a steep refractive-index dispersion of as much as 3.3 x 10(-10) Hz(-1), corresponding to a group velocity of 1800 m/s.

Dark-state imaging for two-dimensional mapping of a magnetic field.

By imaging the dark states that are due to coherent population trapping in Na atomic vapor, we have succeeded in depicting a spatially inhomogeneous magnetic field. Highly resolved dark lines represent cross sections of the surfaces of constant magnetic fields, and they agree well with the predicted hyperfine Zeeman splitting and the two-photon selection rules of the Na atom. Mapping was made two dimensionally in real time, but extension to three dimensions is straightforward. Furthermore, unlike the previous techniques based on optical pumping, this method can be used for any magnetic-field directions.