Nonlinear focusing of picosecond baseband pulses in paraelectric crystals in a wide temperature range

摘要

The nonlinear baseband electromagnetic pulses of a wide spectrum that covers the lower part of terahertz (THz) range are investigated theoretically in the paraelectric crystals like SrTiO_3 at the moderately low temperatures 50-200 K. The frequency dispersion is important there. The dominating nonlinearity of the crystal is cubic. To increase the influence of the nonlinearity, the focusing of the input baseband pulses of small amplitudes has been applied. The main attention is paid to the three-dimensional (3D) geometry of focusing of the input baseband pulses. The nonlinear focusing of input long baseband pulses by the exciting antenna results in the formation of extremely short baseband pulses of subpicosec-ond durations. Under 3D focusing the peak values of the nonlinear focused pulses are bigger and their durations are shorter than ones under 2D focusing, but the transverse localization is stronger under 2D focusing.