On the bifurcation of the circular polarisation of the fifth and seventh pump-field harmonics generated in the plasma produced by the ionisation of a gas of excited hydrogen-like atoms

Within the framework of the Bethe ionisation model we considered theoretically the dependences of the degree of circular polarisation of the fifth and seventh pump-field harmonics, which are generated due to bremsstrahlung, on the electric intensity of the pump field, the degree of its circular polarisation, and the principal quantum number of the excited states of hydrogen-like atoms of a gas ionised by the pump field. A bifurcation of the circular polarisation of these harmonics was discovered, which confirms our previous hypothesis that this effect is common for harmonics generated due to the bremsstrahlung in the pump field when the plasma electrons oscillate in this field. We determined how the relationships under consideration are scaled with V_En/V_Z, the product of electron oscillation velocity and the principal quantum number of the excited electron divided by the Coulomb velocity.