Doubly dressed states in a ladder-type two-photon, three-level coupling system are observed. The electromagnetically induced transparency ͑EIT͒ doublet signal is interpreted as arising from the absorption and gain components of the Mollow spectrum. The separation of the EIT doublet matches the theoretical prediction. A numerical simulation demonstrates that the Doppler velocity group may perturb the light shift from the symmetric center of the EIT doublet. The quantum nature of the EIT system significantly suppresses Doppler broadening.

This paper thoroughly elucidates the relative intensities of the probe transmission in a ladder-type electromagnetically induced transparency (EIT) system by considering the optical pumping effect. The observed EIT spectra reveal a different probe or coupling power dependence for various transmission peaks. In addition to causing quantum interference, the probe and coupling laser fields realign the population of Zeeman sublevels in the ground state through optical pumping. Analytical results indicate that the redistribution levels, failing to contribute to the EIT peaks, either out of transition path or zero transition probability, significantly affect the transmission intensity.

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This investigation clarifies the transition phenomenon between the electromagnetically induced transparency (EIT) and Raman absorption in a ladder-type system of Doppler-broadened cesium vapor. A competition window of this transition was found to be as narrow as 2 MHz defined by the probe Rabi frequency. For a weak probe, the spectrum of EIT associated with quantum interference suggests that the effect of the Doppler velocity on the spectrum is negligible. When the Rabi frequency of the probe becomes comparable with the effective decay rate, an electromagnetically induced absorption (EIA) dip emerges at the center of the power broadened EIT peak. While the Rabi frequency of the probe exceeds the effective decay rate, decoherence that is generated by the intensified probe field occurs and Raman absorption dominates the interaction process, yielding a pure absorption spectrum; the Doppler velocity plays an important role in the interaction. A theory that is based on density matrix simulation, with or without the Doppler effect, can qualitatively fit the experimental data. In this work, the coherence of atom-photon interactions is created or destroyed using the probe Rabi frequency as a decoherence source.

Ladder-type electromagnetically induced transparency (EIT) and two-photon absorption (TPA) under a low-light level of probe (0.2 μW∕cm 2 0.06Γ 2 ) and weak coupling power for a cesium atom at room temperature are investigated. Reduction of the fluorescence on the TPA in a three-level system via EIT interference is clearly observed and analyzed under the low probe Rabi frequency of about 0.30 MHz to avoid the affects from the vicinity of intermediate hyperfine states. The transparency ratio of EIT derived from the reduction of fluorescence is about 25%. Additionally, the EIT linewidth observed can be as narrow as 2.64 MHz, while the coupling Rabi frequency is around 2.66 MHz. By solving the steady-state optical Bloch equations, the numerical simulation spectra are in good agreement with EIT and TPA. According to our investigations, the Doppler velocity averaging effect over the thermal atoms reducing the linewidth of the EIT signal proves the advantage of observing the EIT in the room-temperature cell.