Análise teórica dos efeitos coerentes de transparência e absorção eletromagneticamente induzida em átomos

Abstract

In this work, we did a theoretical model for studying the coherent effects of the electromagnetically induced transparency (EIT) based on the coherent population trapping (CPT) and electromagnetically induced absorption (EIA) associated with the spontaneous transference mechanism of the coherence from the excited state to the ground state in atomic vapor. We consider a semi-classical model, where the atoms are treated like a four-level system interacting with two optical fields (a strong and weak fi eld) in the N type confi guration. We present an analytic and numeric solutions, where we performed a detailed analysis of the EIA and EIT resonances widths as a function of the strong fi eld power for diferent spontaneous transference rate of the coherence from the excited state to the ground state, associated in the model to parameter B. Our results show that, how larger the B value smaller the power broadening from the EIT or EIA resonance. In the extreme case B = 1, we only observe the EIA narrow resonance free from power broadening. On the other hand, the greatest power broadening occurs when we have B = 0, where we only observe the EIT effect and our model is equivalent to A type system. In addition, we have obtained the same results from the analyze of the fluorescence spectrum, showing that the observed narrow resonances have the same behavior as the absorption spectrum of the weak fi eld. Another quite interesting results, we get from our model that it is not possible to identify any coherent effect from the absorption and fluorescence spectrum for some values of B and power of the strong fi eld, this way we determine a curve of B as function of the power of the strong field in this conditions and we show what conditions must be satisfi ed to observe the EIT or EIA signal. To evaluate the analytical solutions we obtained through perturbative methods, we did numerical solution of our set of equations and we get an excellent agreement between the approximate analytical and the exact numerical solutions. One of the applications of the obtained results in this work is to enable the creation of new high-resolution magnetometry techniques and the construction of new atomic memories based in EIA resonances.