Homi Bhabha National Institute, Bhabha Atomic Research Centre, Mumbai 400085, India.
J Chem Phys. 2012 Sep 14;137(10):104309. doi: 10.1063/1.4751445.
Electromagnetically induced transparency (EIT) in a molecular three-level Λ system with permanent dipole moments and undergoing m- and n-photon transitions by pump and probe lasers is investigated. Analytical expressions are derived for probe absorption spectrum and dispersion for a medium of stationary as well as thermal molecules. Contrary to the earlier study by Zhou et al. [J. Chem. Phys. 131, 034105 (2009)], we observe no amplification in 2 + 2 photon process when the sign of the difference of the permanent moments of the excited and the ground levels is reversed. Reasons for these contrasting observations are discussed. Our study shows that the permanent moments essentially damp the laser-molecule Rabi frequency to result in narrower EIT line width and larger group velocity index. These effects are further enhanced when the order of the multi-photon process is increased. The importance of the virtual mechanism is discussed by considering the special case of 2 + 1 photon EIT.
研究了具有永久偶极矩的分子三能级 Λ 系统在泵浦和探测激光作用下通过 m 光子和 n 光子跃迁的电磁感应透明（EIT）现象。推导了处于静态和热分子介质中探测吸收谱和色散的解析表达式。与 Zhou 等人的早期研究[J. Chem. Phys. 131, 034105 (2009)]不同，当激发态和基态的永久偶极矩之差的符号反转时，我们观察不到 2+2 光子过程中的放大。讨论了这些对比观察的原因。我们的研究表明，永久偶极矩实质上会抑制激光与分子的 Rabi 频率，从而导致 EIT 线宽变窄和群速度指数变大。当多光子过程的阶数增加时，这些效应会进一步增强。通过考虑 2+1 光子 EIT 的特殊情况，讨论了虚拟机制的重要性。
