Collinear phase-matched optical rectification is studied in pumped with near-infrared light. The pump-intensity dependence is presented for three crystal lengths (0.3, 1.0, and 3.0 mm) to determine the effects of linear optical absorption, nonlinear optical absorption, and terahertz free-carrier absorption on the generation. Critical parameters such as the coherence length (for velocity matching), dispersion length (for linear pulse broadening), and nonlinear length (for self-phase modulation) are determined for this material. These parameters provide insight into the upper limit of pulse intensity and crystal length required to generate intense terahertz pulses without detriment to the pulse shape. It is found that 1 mm thick , pumped at 1.28 μm with intensity of , will produce intense undistorted pulses, whereas longer crystals or larger intensities modify the pulse shape to varying degrees. Moreover, phase-matching dispersion maps are presented for the terahertz generation over a large tuning range (1.1–2.4 μm) in the longer (3 mm) crystal, demonstrating the phase-matching bandwidth and phase mismatch that leads to fringing associated with multipulse interference. All observed results are simulated numerically showing good qualitative agreement.
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