Time-frequency analysis of two-photon absorption effect during optical rectification in a ZnTe crystal pumped at...

Optical rectification in nonlinear crystals is a well-established method for generating terahertz (THz) waves from ultra-short optical pulses. To achieve high conversion efficiency, the phase-matching conditions between the pump pulse and the generated THz wave within the nonlinear medium must be satisfied. For a ytterbium laser operating at 1.024 µm, a severe phase mismatch occurs in the zinc telluride (ZnTe) crystal, preventing the efficient generation of broadband THz pulses. Using time-frequency analysis, we show that the ultrafast charge carrier dynamic, mainly induced by two-photon absorption, generated in the nonlinear medium during optical rectification processes in ZnTe, plays a crucial role in the filtering of the out-of-phase components of the THz signal, thus enabling the recovery of broadband THz pulse generations.