Features of propagation of the high-intensity femtosecond laser pulses in magnesium and sodium fluoride crystals

The periodic filamentation patterns across and along laser channel tracks, induced by high-intensity femtosecond laser pulses in magnesium and sodium fluoride crystals, have been disclosed. The patterns are rationalized by deterministic vectorial effect, difference in propagations of linearly- and circularly-polarized laser pulses, and appearances of the orbital angular momentum of the light beams due to optical astigmatism. - Highlights: • The periodic pattern of multiple filamentation in the cross-section of the femtosecond laser channel in ionic crystals is shown and explained for the first time. • When the femtosecond laser beam is perpendicular to optical axis of the anisotropic MgF₂ crystal, the single filaments have strictly periodic structure due to inducing change of pulse polarization by the crystal. • The lower efficiency of multiphoton ionization and CCs luminescence in the case of irradiation by circularly polarized femtosecond laser pulses of MgF₂ take place. • In our paper, it is reported for the first time on twisting of the femtosecond laser beam in ionic crystal that can have useful application