Experimental implementation of a four-level N-type scheme for the observation of Electromagnetically Induced Transparency

摘要

A nondegenerate four-level N-type scheme was experimentally implemented toobserve electromagnetically induced transparency (EIT) at the $^{87}$Rb D$_{2}$line. Radiations of two independent external-cavity semiconductor lasers wereused in the experiment, the current of one of them being modulated at afrequency equal to the hyperfine-splitting frequency of the excited 5P$_{3/2}$level. In this case, apart from the main EIT dip corresponding to thetwo-photon Raman resonance in a three-level $\Lambda$-scheme, additional dipsdetuned from the main dip by a frequency equal to the frequency of the HFgenerator were observed in the absorption spectrum. These dips were due to anincrease in the medium transparency at frequencies corresponding to thethree-photon Raman resonances in four-level N-type schemes. The resonanceshapes are analyzed as functions of generator frequency and magnetic field.