Low-light-level ladder-type electromagnetically induced transparency and two-photon absorption

Ladder-type electromagnetically induced transparency (EIT) and two-photon absorption (TPA) under a low-light level of probe (0.2  μW/cm2(0.06Γ2)) 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.