Electromagnetically induced transparency in a Cs 6S-8S two-photon transition

We report the investigation of V-type electromagnetically induced transparency (EIT) in a Cs 6S-8S two-photon transition. This EIT occurs only under a very high coupling intensity due to the weak coupling of two-photon transition. In our experiment, an external cavity diode laser frequency stabilized on the Cs hyperfine transition $|6 ^2S_{1/2}, F=4 \rangle\rightarrow|6 ^2P_{3/2}, F=5\rangle$ is served as a pumping field. The coupling field is a high power tunable Ti:sapphire laser which scanned through the two-photon transitions of Cs $|6 ^2S_{1/2}, F=4\rangle\rightarrow|8 ^2S_{1/2}, F=4\rangle$ at 822 nm. The coupling laser was retro- reflected through a confocal lens system and overlapped with the pump laser at the center of a temperature stabilized Cs cell. The cascade fluorescence from $|7 ^2P_{3/2} \rangle\rightarrow|6 ^2S_{1/2}\rangle$ and the power of transmitted pump laser were monitored simultaneously. An EIT signal of the pump field has been observed while the coupling laser frequency is resonant to the two-photon transition.