THz conversion efficiency in DSTMS limited by high-order nonlinearities

We have studied the THz generation in DSTMS using a quasi-3D model that takes into account high-order nonlinear effects beyond the χ
⁽²⁾
nonlinearity. The nonlinear refractive index (Kerr effect) and three-photon absorption (3PA) coefficients for the wavelength of 1.4 μm utilized in the model were determined by the Z-scan method. The simulation results are in good agreement with the experimentally measured THz and near-infrared spectra, confirming the validity of the proposed model. Our analysis shows that the 3PA process mainly limits THz generation in DSTMS at high pump fluences. The cascaded optical rectification further decreases THz conversion efficiency due to the spectral broadening of the excitation pulse.