The paper evaluates the contribution of the electromagnetically induced transparency (EIT) phenomenon to the processes of the microwave background (CMB) formation in early universe. We found the additional function f to the integrated line absorption coefficient. This makes it the necessity to upgrade the Sobolev escape probability: p ij (τ S) → p ij (τ S · (1 + f)). We calculated the magnitude of the function f for different schemes of the hydrogen atom in the three-level approximation in terms of the field parameters. The electric field amplitudes are defined using the CMB distribution. We found that the contribution of f can be significant in some cases.
 J. P. Marangos, T. Halfmann, In: M. Bass, G. Li, E.V. Stryland (Eds.), Electromagnetically Induced Transparency, Handbook of Optics, Third Edition, vol. IV, Optical Properties of Materials, Nonlinear Optics (Mc Graw Hill, New York, 2010) 14
 Ya. B. Zel’dovich, V. G. Kurt, R. A. Syunyaev, Zh. Eksp. Teor. Fiz. 55, 278 (1968)
 Ya. B. Zel’dovich, V. G. Kurt, R. A. Syunyaev, Sov. Phys. JETP Lett. 28, 146 (1969)
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