Intensity dependence narrowing of electromagnetically induced absorption in a Doppler-broadened medium

We report on magnetic-field induced transparency (MIT) based on Ramsey electromagnetically induced absorption (EIA) in a paraffin-coated Rb vapor cell. Changing the laser polarization from linear to circular in the presence of a weak residual transverse magnetic field to the laser propagation, the narrow absorption due to the Ramsey EIA transformed into the transparency due to MIT of the 5S1/2 (F = 2)-5P3/2 (F' = 3) transition of 87Rb in the paraffin-coated Rb vapor cell. The spectral widths of the EIA and MIT in the Hanle configuration were measured to be 0.6 mG (425 Hz) and 1.2 mG, respectively. MIT depended on the long preservation time of the ground-state coherent spin states and the transverse magnetic field. From the numerical results, the crossover between the Ramsey EIA and the MIT could be illustrated as the superposition of both signals.

Efficient atomic memory using electromagnetically induced absorption

We compared, experimentally and theoretically, Hanle electromagnetically induced absorption (EIA) obtained using Gaussian and $\ensuremath{\Pi}$-shaped laser beams 3 mm in diameter. The study was done by measuring the transmission of a laser locked to the ${F}_{g}=2\ensuremath{\rightarrow}{F}_{e}=3$ transition at the ${D}_{2}$ line of $^{87}\mathrm{Rb}$ in a vacuum cell. EIA linewidths obtained for the two laser profiles were significantly different in the range of laser intensities $1$--$4$ mW/cm${}^{2}$. EIA with the $\ensuremath{\Pi}$-shaped laser beam has a broad intensity maximum and linewidths larger than those obtained with the Gaussian beam profile. We also studied Hanle EIA by measuring the transmission of selected segments of the entire laser beam by placing a small movable aperture in front of the detector. Waveforms so obtained in Hanle EIA resonances were strongly influenced both by the radial distance of the transmitted segment from the beam center and by the radial profile of the laser beam. We show that outer regions of Gaussian beam, and central regions of the $\ensuremath{\Pi}$-shaped beam generate the narrowest lines. The different behaviors of EIA owing to different beam profiles revealed by both theory and experiment indicate the importance of the radial profile of the laser beam for proper modeling of coherent effects in alkali metal vapors.

We study theoretically laser excitation of Rydberg triplet states of strontium atoms in the presence of weak microwave (MW) fields. Starting from the ground state $5s^2\,^1S_0$, the Rydberg excitation is realized through the metastable, triplet $5s5p\,^3P_1$ state, whose decay rate $\gamma_2$ is $2\pi\times 7.5$ kHz, much smaller than the one in the singlet state or alkali atoms. The influences of $\gamma_2$ on the transparency and absorption spectrum in the electromagnetically induced transparency (EIT), and electromagnetically induced absorption (EIA) regime are examined. Narrow transparent windows (EIT) or absorption peaks (EIA) are found, whose distance in the spectrum depends on the Rabi frequency of the weak MW field. It is found that the spectrum exhibits higher contrast than using the singlet state or alkali atoms in typical situations. Using the metastable intermediate state, we find that resonance fluorescence of Sr gases exhibits very narrow peaks, which are modulated by the MW field. When the MW field is weaker than the probe and control light, the spectrum distance of these peaks are linearly proportional to $\Omega_m$. This allows us to propose a new way to sense very weak MW fields through resonance fluorescence. Our study shows that the Sr triplet state could be used to develop the Rydberg MW electrometry that gains unique advantages.

In this paper we describe experimentally and theoretically the increase in the electromagnetically induced absorption (EIA) resonance under the influence of an additional optical field. EIA was observed on the cycling transition of the rubidium ${\text{D}}_{2}$ line in the Hanle configuration in the presence of the second-laser field acting on an open transition coupled with a cycling one via a common ground state. We present results obtained for different polarization orientations and propagation directions of the two laser beams. A systematic theoretical analysis based on the optical Bloch equations explains most of the experimental data. A lot of attention is also paid to a qualitative understanding of the EIA---its resonance shape, amplitude, and the response to the additional optical fields.

The propagation of a probe field through a four-level Y-type atomic system is described in the presence of two additional coherent radiation fields, namely, the control field and the coupling field. An expression for the probe response is derived analytically from the optical Bloch equations under steady state condition to study the absorptive properties of the system under probe field propagation through an ensemble of stationary atoms as well as in a Doppler broadened atomic vapor medium. The most striking result is the conversion of electromagnetically induced transparency (EIT) into electromagnetically induced absorption (EIA) as we start switching from weak probe regime to strong probe regime. The dependence of this conversion on residual Doppler averaging due to wavelength mismatch is also shown by choosing the coupling transition as a Rydberg transition.

A three-level lambda system driven by multicolor control, pump, and probe fields is investigated. The pump and probe fields are derived from the same laser with opposite propagating directions. Due to the Doppler effect, the zero group-velocity atoms face bichromatic fields, while other atoms face trichromatic fields. The atomic medium shows distinct characteristics and exhibits simultaneous electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) at two frequencies. EIT and EIA peaks have a fixed relationship with frequency, which is determined by the Doppler shifts.

EIT line shape in an open and partially closed multilevel V-type system

Standing wave pump field induced coherent non-linear resonances in rubidium vapor

Quantum interference effects in a multi-driven transition Fg = 3 ↔ Fe = 2

Enhanced effects of subluminal and superluminal propagation

The explanation presented by Taichenachev et al. [Phys. Rev. A $61,$ 011802 (2000)] according to which the electromagnetically induced absorption (EIA) resonances observed in degenerate two-level systems are due to coherence transfer from the excited to the ground state is experimentally tested in a Hanle-type experiment observing the parametric resonance on the $D1$ line of ${}^{87}\mathrm{Rb}.$ While EIA occurs in the $F=\stackrel{\ensuremath{\rightarrow}}{1}{F}^{\ensuremath{'}}=2$ transition in a cell containing only Rb vapor, collisions with a buffer gas (30 torr of Ne) cause the sign reversal of this resonance as a consequence of collisional decoherence of the excited state. A theoretical model in good qualitative agreement with the experimental results is presented.

We investigate the atomic four-level $N$ configuration both analytically and numerically, for various pump and probe intensities, with and without transfer of coherence (TOC) and Doppler broadening, and compare the results obtained to those of realistic atomic systems. We find that TOC affects the whole spectrum, in addition to producing an electromagnetically induced absorption (EIA) peak at line center. We show that the EIA peak splits as the pump intensity increases. These results are compared with those of realistic systems. When the pump is ${\ensuremath{\sigma}}^{+}$ polarized and the probe is $\ensuremath{\pi}$ polarized, the results are similar to those of the $N$ configuration. When the pump and probe polarizations are both linear with perpendicular polarizations, various $N$-like subsystems contribute to the spectrum. Consequently, the splitting of the EIA peak only occurs at very high pump intensities. We also discuss the influence of the probe on the pump absorption and refraction and find that both the pump and probe show EIA peaks when the pump intensity is low, and complementary behavior when the pump is intense. At both low and high pump intensity, the pump and probe dispersions are of opposite sign.

We report on switching the intensity correlation or anticorrelation by changing the polarization basis for measuring light that has already propagated through the electromagnetically induced transparency (EIT) medium of the 5S1/2 (F = 2) − 5P1/2 (F ′ = 1) transition of 87Rb atoms. When a linearly polarized laser beam interacts with the EIT medium in the Hanle configuration, selection of the polarization basis after the optical field has already interacted with the atoms was found to significantly affect the intensity-intensity correlation of the two orthogonal polarization components. We compared the second-order correlation functions of two postselected polarization bases (linear and circular), and the polarization basis effect on the second-order correlation functions as a function of the applied magnetic field was numerically calculated using an eight-level atomic model.

Refractive index control and its relevance to the velocity-selective effect generated by the propagation direction of the incoherent pumping field are studied in an open V-type atomic system. The velocity-selective effect on electromagnetically-induced transparency (EIT) is presented in theory and verified in the experiment. It shows that, in contrast to the case of copropagation, counter-propagation of the incoherent pumping field has an absolutely opposite effect on the dispersion of the V-type EIT system. The experimental results are in good agreement with the theoretical analysis.