Gy. Toth | Searcharxiv

arXiv2017

Mapping the lattice-vibration potential using terahertz pulses

We develop a method for mapping the anharmonic lattice potential using the time-dependent electric field of the transmitted pulse through thin sample supported by a substrate of non-negligible thickness. Assuming linear propagation in the substrate we fully take into account internal reflection in it while the sample can show arbitrary nonlinear response. We examine the effect of frequency averaging appropriate for broad-band pulse and compare the results taking into account the full frequency dependence. We illustrate the procedure applying it to a model based on recently observed ferroelectric soft-mode nonlinearity in SrTiO$_3$.

physics.optics↗

arXiv2015

Interplay of diffraction and nonlinear effects in propagation of ultrashort pulses

We investigate the interplay of diffraction and nonlinear effects during propagation of very short light pulses. Adapting the factorization approach to the problem at hand by keeping the transverse-derivative terms apart from the residual nonlinear contributions we derive an unidirectional propagation equation valid for weak dispersion and reducing to the slowly-evolving-wave-approximation for the case of paraxial rays. Comparison of numerical simulation results for the two equations shows pronounced differences when self-focusing plays important role. We devote special attention to modelling propagation of ultrashort terahertz pulses taking into account diffraction as well as Kerr type and second order nonlinearities. Comparing measured and simulated wave forms we deduce the value of the nonlinear refractive index of lithium niobate in the terahertz region to be three orders of magnitude larger than in the visible.

physics.optics↗