  The repartition of redshifts of the lines observed in the spectra of the
quasars is generally considered as stochastic, but several authors showed that
the difference of two redshifts is the product of an integer by a basic
redshift zf = 0.062. This property results from a coherent Raman effect during
the propagation of the incoherent light in a halo of atomic hydrogen, without
any jet of gas, or dark matter. The coherence forbids a blur of the images or
of the spectra. The computation of zf does not require any new spectroscopic
parameter. The non-linearity of the combination of Lyman absorptions and
coherent Raman effect explains both the observed positions of the spectral
lines and their high contrast.
