Birefringence Effect as a Tool for Astrophysical Plasma Study

Group delay between two magnetoionic modes is discovered and spectrally confirmed ( $\Delta t_g\propto f^{-3\mathrm{}}$) for the first time for quasiperiodic narrow band millisecond solar radio pulsations. Analysis of cross delays and autodelays proves that both $X$ and $O$ modes originate at the same source, so the radiation is weakly polarized originally. This finding allows one to specify the emission mechanism of the pulsations to be a nonlinear plasma mechanism operating at the second harmonics. Physical parameters of the solar corona are determined by the use of the theory of the nonlinear plasma mechanism; they agree well with independent observations of solar millisecond pulsations.