On self-focusing and defocusing of few-cycle pulses in hydrogen-containing ferroelectrics

The role of diffraction in the propagation of few-cycle pulses is studied in hydrogen-containing ferroelectrics in the case of the active role of optical electronic and tunnelling transitions. It is shown that, unlike optical electronic transitions, tunnelling proton transitions can produce the defocusing effect if they are overlapped by the spectral components of the pulse. The parameters of a medium and the pulse are estimated at which the defocusing effect dominates over self-focusing. It is shown that nonresonance quasi-monochromatic pulses in the optical range are subjected to self-focusing in such media.