<title>Electromagnetically induced transparency, electromagnetically induced absorption, and giant Kerr effect in closed degenerate two-level systems</title>

Abstract

Spontaneous transfer of coherence has proven to be a good interpretative scheme for the explantation of the spectra of a probe laser probing a closed degenerate two-level systems. With its aid it was possible to give an explanation for the emergence of electromagnetically induced absorption and also to make predictions on the associated coupling laser spectra. Here we extend our work on the role of the coupling laser in electromagnetically induced absorption presenting new measurements of the probe and coupling laser absorption and dispersion spectra - taken in the D₂ line of caesium - which reassert the importance of spontaneous transfer of coherence in the generation of electromagnetically induced absorption spectra. All measurements were performed with linearly polarised coupling and probe laser of orthogonal polarisation, acting on a perpendicularly propagating caesium atomic beam to minimise the Doppler broadening of the lines. For sake of completeness we compared the electromagnetically induced absorption spectra with electromagnetically induced transparency spectra obtained in another two-level system within the same line. The measured probe spectra were used to calculate the refractive index of caesium in the presence of electromagnetically induced transparency and absorption. On that basis we could calculate the effect of Kerr nonlinearities and measure nonlinear Kerr coefficients of the order of <i>n</i>₂ &ap; 10^-5 cm²/mW with absorption coefficients of the order of &agr; &ap; 0.1 cm^-1.