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Influence of Pump Laser Phase and Amplitude Distortions on Terahertz Generation Efficiency

We analyze the impact of phase front and intensity profile distortions of the pump laser on the generation of narrowband terahertz radiation by difference frequency generation in periodically poled Lithium Niobate (PPLN). A code employing finite difference method for beam propagation and nonlinear interaction in cylindrical symmetric system is developed. The simulation accounts for difference frequency generation, self-focusing, self-phase modulation, diffraction, dispersion and terahertz absorption. We find that terahertz generation in PPLN crystals shows negligible sensitivity to spatial intensity modulation. In contrast, phase front modulations may drastically reduce the terahertz generation efficiency. Thus, care must be taken to avoid large phase distortions in high power laser beams for laser-driven terahertz sources.