Comparison of wavelength dependence in cascade-, Λ-, and Vee-type schemes for electromagnetically induced transparency

We present a theoretical study of the effects of mismatching wavelengths for the coupling and probe fields in Doppler-broadened media for the three basic energy level configurations commonly used to realize electromagnetically induced transparency (EIT). Three wavelength regimes are considered: mismatched wavelengths for which the coupling frequency is greater than the probe frequency, matched wavelengths for which the coupling and probe frequencies are equal, and mismatched wavelengths for which the probe frequency is greater than the coupling frequency. The transparency that may be induced in these regimes is compared for the cascade-, Lambda-, and Vee-type systems. We show that in the first mismatched regime (lambda(c) < lambda(p)) EIT is possible in all schemes and is in fact stronger than in the matched case. It is also demonstrated that for the second mismatched regime (lambda(c) > lambda(p)) EIT can be realized most readily in the Vee-type configuration in the presence of Doppler broadening. These predictions are explained by considering the absorption as a function of both the probe field detuning and the atomic velocity. [S1050-2947(99)01006-9].