Interplay of diffraction and nonlinear effects in the propagation of ultrashort pulses

Korpa, Csaba and Tóth, György and Hebling, János (2016) Interplay of diffraction and nonlinear effects in the propagation of ultrashort pulses. Journal of Physics B: Atomic, Molecular and Optical Physics. ISSN 0953-4075, ESSN: 1361-6455

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Abstract

We investigate the interplay of diffraction and nonlinear effects during the 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 which is valid for weak dispersion and reduces to the slowly-evolving-wave-approximation in the case of paraxial rays. A comparison of the numerical simulation results for the two equations shows pronounced differences when selffocusing plays an important role. We devote special attention to modelling the propagation of ultrashort terahertz pulses taking into account diffraction as well as Kerr-type and second-order nonlinearities. Comparing the 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 part of the spectrum.

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