Formation of short terahertz electromagnetic pulses in nonlinear paraelectrics

The nonlinear electromagnetic (EM) phenomena in terahertz (THz) range in the crystalline SrTiO₃ are investigated theoretically. The goal is to investigate possibilities of the forming of short THz EM pulses. The moderate cooling T ≈ 77 K is considered. The self-action of input long envelope and baseband pulses leads to the modulation instability due to the cubic nonlinearity and frequency dispersion and to the generation of the regular sequences of short THz envelope or baseband pulses at the output of the crystal. Under the resonant nonlinear interaction of two counterpropagating EM waves with the acoustic wave of the difference frequency also the modulation instability occurs that leads to the chaotic wave modulation.