Dark and bright Doppler-free resonances observed in atomic vaporXiao-Gang Wei1, 2, Jin-Hui Wu1, 2, Hai-Hua Wang1, 2, Ang Li1, 2, Zhi-Hui Kang1, 2, Yun Jiang1, 2 and Jin-Yue Gao1, 2
1 College of Physics, Jilin University - Changchun 130023, PRC
2 Key Laboratory of Coherent Light and Atomic and Molecular Spectroscopy of Ministry of Education, Jilin University - Changchun 130023, PRC
received 26 January 2007; accepted in final form 7 April 2007; published May 2007
published online 3 May 2007
We investigate an inhomogeneously broadened four-level atomic system driven by two strong coherent fields and probed by a weak laser. By carefully adjusting strengths of the driving fields, we can observe a greatly enhanced peak between two dark resonances in the probe absorption spectrum. The enhanced absorption peak will split into two lower ones and then result in a third dark resonance if we gradually weaken one driving field. Ultimately, the whole probe absorption spectrum evolves towards the usual EIT spectrum with only one dark resonance. Based on appropriate numerical calculations and qualitative analysis, we show that the experimental results can be well understood by separately considering the probe absorptions arising from partial atoms with different velocities.
42.50.Gy - Effects of atomic coherence on propagation, absorption, and amplification of light; electromagnetically induced transparency and absorption .
42.50.Hz - Strong-field excitation of optical transitions in quantum systems; multiphoton processes; dynamic Stark shift .
© Europhysics Letters Association 2007